Patent Publication Number: US-8116075-B2

Title: Disk-drive systems that move data to spare drives from drives about to fail and method

Description:
CROSS-REFERENCES TO RELATED INVENTIONS 
     This is a divisional of U.S. patent application Ser. No. 11/537,610, filed Sep. 30, 2006 and titled “DISK-DRIVE SYSTEMS WITH A VARYING NUMBER OF SPARES FOR DIFFERENT EXPECTED LIFETIMES AND METHOD,” which will be issued as U.S. Pat. No. 7,702,502 on Apr. 20, 2010, and which is a divisional of U.S. patent application Ser. No. 11/027,777, filed Dec. 29, 2004 and titled “SYSTEM AND METHOD FOR MASS STORAGE USING MULTIPLE-HARD-DISK-DRIVE ENCLOSURE,” which issued as U.S. Pat. No. 7,167,359 on Jan. 23, 2007, and which claims benefit of U.S. Provisional Patent Application No. 60/580,987, filed Jun. 18, 2004 and titled “SYSTEM AND METHOD FOR REDUCED VIBRATION INTERACTION IN A MULTIPLE-HARD-DISK-DRIVE ENCLOSURE,” and of U.S. Provisional Patent Application No. 60/533,605, filed Dec. 29, 2003 and titled “SYSTEM AND METHOD FOR IMPROVED HARD-DISK-DRIVE DATA-STORAGE ENCLOSURE,” each of which is hereby incorporated by reference in its entirety. 
     This application is also related to U.S. patent application Ser. No. 11/026,553, filed Dec. 29, 2004 and titled “SYSTEM AND METHOD FOR REDUCED VIBRATION INTERACTION IN A MULTIPLE-DISK-DRIVE ENCLOSURE,” which issued as U.S. Pat. No. 7,280,353 on Oct. 9, 2007, which is incorporated herein by reference in its entirety. 
     This application is additionally related to: 
     U.S. patent application Ser. No. 11/537,600 filed on Sep. 29, 2006 and entitled “DISK-DRIVE ENCLOSURE HAVING FRONT-BACK ROWS OF SUBSTANTIALLY PARALLEL DRIVES AND METHOD” (which issued as U.S. Pat. No. 7,349,205 on Mar. 25, 2008); 
     U.S. patent application Ser. No. 11/537,605 filed on Sep. 29, 2006 and entitled “DISK-DRIVE ENCLOSURE HAVING ROWS OF ALTERNATELY FACING PARALLEL DRIVES TO REDUCE VIBRATION AND METHOD” (which issued as U.S. Pat. No. 7,359,188 on Apr. 15, 2008); 
     U.S. patent application Ser. No. 11/537,606 filed on Sep. 29, 2006 and entitled “DISK-DRIVE ENCLOSURE HAVING LATERALLY OFFSET PARALLEL DRIVES TO REDUCE VIBRATION AND METHOD” (which issued as U.S. Pat. No. 7,391,609 on Jun. 24, 2008); 
     U.S. patent application Ser. No. 11/537,608 filed on Sep. 30, 2006 and entitled “DISK-DRIVE ENCLOSURE HAVING NON-PARALLEL DRIVES TO REDUCE VIBRATION AND METHOD” (which issued as U.S. Pat. No. 7,630,196 on Dec. 8, 2009); 
     U.S. patent application Ser. No. 11/537,614 filed on Sep. 30, 2006 and entitled “DISK-DRIVE ENCLOSURE HAVING PAIR-WISE COUNTER-ROTATING DRIVES TO REDUCE VIBRATION AND METHOD” (which issued as U.S. Pat. No. 7,505,264 on Mar. 17, 2009); 
     U.S. patent application Ser. No. 11/537,598 filed on Sep. 29, 2006 and entitled “DISK-DRIVE ENCLOSURE HAVING DRIVES IN A HERRINGBONE PATTERN TO IMPROVE AIRFLOW AND METHOD” (which issued as U.S. Pat. No. 7,319,586 on Jan. 15, 2008); 
     U.S. patent application Ser. No. 11/537,603 filed on Sep. 29, 2006 and entitled “DISK-DRIVE SYSTEM HAVING MULTIPLE POWER SUPPLIES AND MIRRORING AND METHOD” (which issued as U.S. Pat. No. 7,447,015 on Nov. 4, 2008); 
     U.S. patent application Ser. No. 11/537,607 filed on Sep. 30, 2006 and entitled “DISK-DRIVE SYSTEM SUPPORTING MASSIVELY PARALLEL VIDEO STREAMS AND METHOD” (which issued as U.S. Pat. No. 7,626,805 on Dec. 1, 2009); and 
     U.S. patent application Ser. No. 11/537,613 filed on Sep. 30, 2006 and entitled “POROUS LIGHT-EMITTING DISPLAY WITH AIR FLOW THROUGH DISPLAY, ITS USE IN A DISK-DRIVE SYSTEM AND METHOD” (which issued as U.S. Pat. No. 7,646,597 on Jan. 12, 2010); which are all hereby incorporated by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to hard-disk-drive data-storage systems and methods, and more particularly, to high-reliability enclosures that hold a large number of disk drives including spare drives and provide a large number of serial data interfaces operating in parallel, wherein if a drive has failed or has been detected to be in a condition that indicates the drive is about to fail, the data from that drive is reconstructed (for example, the data is copied from a drive that mirrors the data on the failed drive) and placed on one of the spare drives, that from then on, that spare is used in place of the failed drive, resulting in, among other things, improved performance, reliability, manufacturing costs, and/or operational costs. 
     BACKGROUND OF THE INVENTION 
     Massive amounts of data storage are required for many emerging and existing applications. For example, video-on-demand applications can provide access to hundreds or thousands of movies for hundreds or thousands of users simultaneously, requiring vast amounts of digital storage, fast access, 24 hours-per-day and 7 days per week (24/7) availability and uptime, and huge bandwidth. Modern supercomputers also require these features, as well as requiring even faster access, extraordinary data integrity, error checking and error correction. 
     Semiconductor memories provide very fast access, reasonable densities, and moderate costs. However, most common semiconductor memories are volatile (they lose their data when not powered or not refreshed on a timely basis), they develop soft errors (errors that can be corrected by re-writing the affected location) due to various causes including alpha radiation, and they can be cost prohibitive. Additionally, the heat and power requirements can be problematic, if they are used to store vast amounts of information for long time periods. 
     Hard-disk drives (HDDs, also called just “disk drive” or “drive”)) provide cost-effective non-volatile data storage on rotating media. Data are written and read by magnetic transducer heads that are moved to one of thousands of tracks to locate requested data. There are time penalties incurred to move the head to the requested track, to rotate the disk to the requested location on that track, and to serially read or write the data from or to the track location. The moving parts of a disk drive are prone to wear and failure over time. For applications requiring high reliability (error-free data) and availability (24/7 uptime), data can be stored in a redundant manner (e.g., redundant arrays of inexpensive disks, or RAID), and several different RAID schemes are known to the art, frequently making compromises between performance, cost, and data recoverability. Another requirement for many applications is serviceability—the ease of repairing a faulty system in the field (i.e., at a customer&#39;s location of the equipment). 
     Data storage servers (enclosures having one or more disk drives as well as a data processor to receive data access requests and control the storing and fetching of data to and from the disk drives) and storage vaults (enclosures having one or more disk drives but essentially no processor, and using a data processor housed in a separate enclosure to receive data access requests and control the storing and fetching of data to and from the disk drives) can be implemented in free-standing units (typically an upright unit placed on the floor or on a desk) or as rack-mount units (typically horizontally-oriented units bolted to a standardized nineteen-inch (48.26 cm) rack). 
     Typical conventional rack-mount disk-drive enclosures arrange a plurality (3 to 14) HDDs in removable carriers that are accessible from the “front” of the unit (the side typically facing a user area), and usually are arranged so that data and power cables are accessible from the “back” of the unit. The disk drives can thus be replaced fairly easily if one were to fail. RAID solutions can be utilized to use redundant data artifacts to compute the data that was on the failed disk drive. This data is sent to a requestor or used to recreate the data on a new (spare) disk drive once one is inserted to replace the failed unit. Since racks of rack-mount units are often installed in rows, there is typically no access provided from the sides of a rack-mount unit, and since the rack-mount units are stacked one on top of another in each rack there is typically no access provided from the top or bottom of a rack-mount unit. 
     High-density packaging of HDDs in an enclosure exacerbates drive-to-drive vibration interaction problems. With several HDDs, packaged closely together in single enclosure, potentially many doing simultaneous head-seeks, the vibration interaction problem is greatly increased. Previous systems and methods to package HDDs and reduce drive-to-drive vibration interaction involved mechanical stiffening of the enclosure and/or lower density packaging options. 
     Numerous computer applications utilize multiple disk drives for data storage and acquisition. These multiple disk drives are often located in separated locations. For example, disk drives may be arranged in rack systems that consume large amounts of space and require multiple cabinets to house the rack systems. Furthermore, positioning multiple disk drives in separate locations adds to the complexity of data acquisition from the disk drives because a more complex interface with the multiple disk drives is required. In addition, longer cabling is required to reach the separately located disk drives. Accordingly, what is needed is an apparatus that positions multiple disk drives in a manner that simplifies data acquisition from the disk drives and reduces the space needed to house the multiple disk drives. 
     SUMMARY OF THE INVENTION 
     In some embodiments, the present invention generally involves housing a large number of disk drives in an enclosure. In other embodiments, the invention is based on positioning disk drives such that forces occurring during seek and write functions within a first disk drive are counteracted by analogous forces occurring in one or more other drives that are positionally paired with the first disk drive in some embodiments. An example of such a force includes rotation and counter-rotation of disks that is caused by movement of an actuator arm within the disk drive that occurs during a seek or write function of the disk. Other examples of such forces include vibrational forces, rotational, counter-rotational forces, and the like that are due to the movement of a disk within a disk drive. These forces can be caused by numerous actions within a disk drive. Arranging the disk drives according to the invention helps to reduce detrimental results caused by such forces that can increase the incidence of read and write errors. Accordingly, the invention can be used to position multiple disk drives so that the disk drives have a reduced read and write error rate. 
     In some embodiments, the invention provides an apparatus that includes a substrate, and a plurality of disk drives each coupled electrically and mechanically to the substrate, the plurality of disk drives including at least a first and a second disk drive, wherein the first disk drive is positioned relative to the second disk drive so that a rotational force produced by the first disk drive is at least partially counteracted by a rotational force produced by the second disk drive. 
     In other embodiments, the invention provides a method that includes mounting a plurality of drives in an enclosure, the enclosure including a connector substrate, the plurality of drives including at least a first disk drive and a second disk drive that are each electrically and mechanically coupled to the enclosure; and mechanically coupling the first drive and the second drive such that rotational force produced by the first disk drive is at least partially counteracted by rotational force produced by the second disk drive. 
     In some embodiments, the invention provides an apparatus that includes an enclosure that includes a substrate, a means in the enclosure for mounting a plurality of disk drives to the enclosure, and a means for coupling a plurality of disk drives electrically and mechanically to the substrate, the plurality of disk drives including at least a first and a second disk drive, wherein the first disk drive is positioned relative to the second disk drive so that a rotational force produced by the first disk drive is at least partially counteracted by a rotational force produced by the second disk drive. 
     In some embodiments, the invention provides an apparatus that includes a substrate, and a plurality of disk drives each coupled electrically and mechanically to the substrate, the plurality of disk drives including at least a first disk drive and a second disk drive, wherein the first and second disk drive each have a first major face surrounded by a first, second, third and fourth edge and having a first, second, third and fourth corner, wherein the first disk drive and the second disk drive are positioned such that a rotational force produced by the first disk drive is conveyed primarily as a translational force to the second disk drive. 
     In some embodiments, the invention provides a method that includes mounting a plurality of drives in an enclosure, the plurality of drives including at least a first disk drive and a second disk drive that are each electrically and mechanically coupled to the enclosure, and mechanically coupling the first disk drive and the second disk drive such that rotational force produced by the first disk drive is at least partially transmitted as translational force to the second disk drive. 
     In some embodiments, the invention provides an apparatus that includes a substrate; and a means for mounting a plurality of disk drives to the substrate; and a means for coupling a plurality of disk drives electrically and mechanically to the substrate, the plurality of disk drives including at least a first disk drive and a second disk drive, wherein the first and second disk drive each have a first major face surrounded by a first, second, third and fourth edge and having a first, second, third and fourth corner, wherein the first disk drive and the second disk drive are positioned such that a rotational force produced by the first disk drive is conveyed primarily as a translational force to the second disk drive. 
     In some embodiments, the invention provides an apparatus that includes a substrate, and a plurality of disk-drive connectors each coupled electrically and mechanically to the substrate, the plurality of disk-drive connectors including at least a first and a second disk-drive connector, wherein the first disk-drive connector is positioned relative to the second disk-drive connector so that a rotational force produced by a first disk drive that is connected to the first disk-drive connector is at least partially counteracted by a rotational force produced by a second disk drive that is connected to the second disk-drive connector. 
     In some embodiments, the invention provides an apparatus that includes a substrate, and a plurality of disk-drive connectors each coupled electrically and mechanically to the substrate, the plurality of disk-drive connectors including at least a first disk-drive connector and a second disk-drive connector, wherein the first disk-drive connector and the second disk-drive connector are positioned such that a rotational force produced by a first disk drive connected to the first disk-drive connector is conveyed primarily as a translational force to a second disk drive connected to the second disk-drive connector. 
     In some embodiments, the invention provides a method that includes mounting a plurality of disk-drive connectors in an enclosure, the enclosure including a connector substrate, the plurality of disk-drive connectors including at least a first disk-drive connector and a second disk-drive connector that are each electrically and mechanically coupled to the enclosure, and mechanically coupling the first disk-drive connector and the second disk-drive connector such that rotational force produced by a first disk drive that is connected to the first disk-drive connector is at least partially counteracted by rotational force produced by a second disk drive that is connected to the second disk-drive connector. 
     In some embodiments, the invention provides a method that includes mounting a plurality of disk-drive connectors in an enclosure, the plurality of disk-drive connectors including at least a first disk-drive connector and a second disk-drive connector that are each electrically and mechanically coupled to the enclosure, and mechanically coupling the first disk-drive connector and the second disk-drive connector such that rotational force produced by a first disk drive that is connected to the first disk-drive connector is at least partially transmitted as translational force to a second disk drive that is connected to the second disk-drive connector. 
     In some embodiments, the invention provides a method that includes mounting a plurality of disk drives in an enclosure, the enclosure including a connector substrate, the plurality of disk drives including at least a first disk drive and a second disk drive; vibrationally coupling the first disk drive to the second disk drive, and sending a first seek operation to the first disk drive and a second seek operation to the second disk drive, wherein a timing of the first seek operation relative to the second seek operation is adjusted to minimize adverse vibrational interaction between the first disk drive and the second disk drive. 
     In some embodiments, the invention provides an apparatus that includes a data structure having a plurality of entries, each entry containing vibration-interaction information relative to a read operation occurring on a first disk drive of a pair of disk drives and a seek operation being performed on a second disk drive of the pair. 
     In some embodiments, the invention provides an apparatus that includes a memory, the memory holding vibration-interaction information, an information processing unit operatively coupled to the memory to receive the vibration-interaction information and adjusting a timing of seek operations to a plurality of disk drives based on the information. 
     In some embodiments, the invention provides a method that includes mounting a plurality of disk drives in shock mounts in an enclosure and “detenting” the plurality of disk drives against vibration using a disengagable detent device. 
     In some embodiments, the invention provides an apparatus that includes an enclosure, a substrate held within the enclosure, a plurality of disk-drive connectors each coupled mechanically to the substrate, the plurality of disk-drive connectors including at least a first and a second disk-drive connector, and an over-shock detector operatively coupled to the enclosure and adapted to detect and store information regarding one or more over-shock events. 
     In some embodiments, the invention provides a method that includes analyzing vibration-interaction between a plurality of disk drives held in an enclosure and storing information that is based on the analysis into a data structure. 
     In some embodiments, the invention provides a method that includes mounting a plurality of disk drives to disk-drive connectors within an enclosure, adhering a resilient sheet across the plurality of disk drives, and attaching a cover to the resilient sheet. 
     In some embodiments, the invention provides an apparatus that includes a plurality of disk drives mounted to disk-drive connectors within an enclosure, a resilient sheet (such as a visco-elastic membrane, for example) across the plurality of disk drives, and a cover. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various features and attendant advantages of the present invention will become fully appreciated as the invention becomes better understood upon reading the following description and when considered in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the several views. 
         FIG. 1  is a perspective drawing of disk drive  120  mounted in a perpendicular-to-the-major-face orientation (e.g., vertical, if the major face is horizontal) in a disk-drive system  100 . 
         FIG. 2  is a perspective drawing of a storage system  200  with the disk drives placed in a new physical-layout pattern  250  that enables the disk drives themselves to serve as the “fins” of a large heat sink. 
         FIG. 3A  is a block diagram of a power supply  300 , as used in some embodiments. 
         FIG. 3B  is a block diagram of a power supply  300 ′, as used in some embodiments. 
         FIG. 3C  is a block diagram of a power supply  300 ″, as used in some embodiments. 
         FIG. 4A  is a perspective drawing of disk drives  120  and  120 ′ mounted in a vertical orientation in a disk-drive system  100 . 
         FIG. 4B  is a perspective drawing of a pair of disk drives in a T orientation. 
         FIG. 4C  is a perspective drawing of a pair of disk drives in a Y orientation. 
         FIG. 4D  is a perspective drawing of a pair of disk drives in a counter-rotating parallel orientation with their axes of rotation aligned. 
         FIG. 4E  is a perspective drawing of a pair of disk drives in a counter-rotating parallel orientation with their edges aligned. 
         FIG. 4F  is a perspective drawing of a pair of disk drives in a counter-rotating parallel orientation each with its axis of rotation aligned with an edge of the other disk drive. 
         FIG. 4G  is a plan-view schematic of a herringbone configuration  400 ′ with counter-rotating pairs of disk drives. 
         FIG. 5  is a plan-view schematic of a herringbone configuration  500  with counter-rotating pairs of disk drives. 
         FIG. 6A  is a plan-view schematic of another herringbone configuration  600  with counter-rotating pairs of disk drives. 
         FIG. 6B  is a plan-view schematic of another herringbone configuration  601  with counter-rotating pairs of disk drives. 
         FIG. 7A  shows a plan view of yet another herringbone configuration  700  of disk drives. 
         FIG. 7B  shows a perspective view of system  700 . 
         FIG. 8A  is a perspective drawing of prior-art “high-density” hard-disk-drive (HDD) enclosure systems  81  and  82  as might be mounted in a rack  80 . 
         FIG. 8B  is a perspective drawing of a high-density HDD enclosure system  810  according to the present invention. 
         FIG. 8C  is a perspective drawing of a high-density HDD enclosure system  811  using a herringbone configuration according to the present invention. 
         FIG. 8D  is a perspective view that illustrates a perforated support grid for a plurality of disk drives with ESD-(electro-static discharge prevention)-coated visco-elastomeric material. 
         FIG. 8E  is a top view that illustrates nesting support grid for a plurality of disk drives with ESD-(electro-static discharge prevention)-coated visco-elastomeric material. 
         FIG. 8F  is a perspective view that illustrates system  804  having a molded-in connector  819  support for a plurality of drives mounted in a vertical orientation. 
         FIG. 8G  is a top view of system  804  of  FIG. 8F . 
         FIG. 8H  is top view that illustrates the distribution of temperature sensors around the inlet manifold  1112 , outlet manifold  1114  and between-drive spaces  95 . 
         FIG. 8I  is a front view that illustrates the status-display grid  816 . 
         FIG. 8J  is a perspective view that illustrates a cover-latching mechanism that seats the drives into their connectors. 
         FIG. 9A  is a perspective view that illustrates a porous display having LEDs mounted on a screen that has much space for air flow through the displays. 
         FIG. 9B  is a perspective view that illustrates an LCD display mounted on the inlet air dams allowing much space for air flow around the displays. 
         FIG. 9C  is a front-elevation view that illustrates an LCD display mounted on the inlet air dams allowing much space for air flow around the displays. 
         FIG. 10  is a blown-up perspective view of a system  1000  of some embodiments having one or more disk-drive systems  1001  operatively coupled to one or more central processing units (CPU)  1002  and/or one or more video-streaming units  1003  or some combination thereof. 
         FIG. 11  is a plan-view block diagram of a data-storage system  1100  of some embodiments of the invention that provides a high density enclosure having one or more rows of disk drives. 
         FIG. 12  is a plan-view block diagram of a data-storage system  1200  of some embodiments of the invention that uses tapered inlet and outlet air chambers. 
         FIG. 13  is a plan-view block diagram of a data-storage system  1300  of some embodiments of the invention that uses curving tapered inlet and outlet air chambers. 
         FIG. 14  is a plan-view block diagram of a data-storage system  1400  of some embodiments of the invention that uses curving tapered inlet and outlet air chambers, and laterally offset paired drives. 
         FIG. 15  is a plan-view block diagram of a connector circuit card pair  1500  used in some embodiments of the invention. 
         FIG. 16A  is a plan-view block diagram of a data-storage system  1600  of some embodiments of the invention that provides a high density enclosure having four rows of disk drives. 
         FIG. 16B  is a functional block diagram of a circuit  1608  used in some embodiments of system  1600 . 
         FIG. 16C  is a functional block diagram of a circuit  1609  used in some embodiments of system  1600 . 
         FIG. 17  is a plan-view block diagram of a data-storage system  1700  of some embodiments of the invention that provides a high density enclosure having one or more rows of disk drives accommodating a variable number of disk drives in each row. 
         FIG. 18  is a perspective-view block diagram of a data-storage system  1800  of some embodiments of the invention that provides one or more rows of disk drives in an upper portion of the enclosure and one or more power supplies in an adjacent lower portion of the enclosure. 
         FIG. 19  is an elevation view of a data-storage system  1900  of some embodiments of the invention that provides a high-density enclosure having one or more rows of disk drives. 
         FIG. 20A  is an elevation view of a data-storage system  2000  of some embodiments of the invention that provides a high-density enclosure having one or more rows of disk drives arranged in coupled pairs of counter-rotating disk drives. 
         FIG. 20B  is an elevation view of a data-storage system  2001  of some embodiments of the invention that provides a high-density enclosure having one or more rows of disk drives with an adjustable-height mid-drive vibration damper  2075 . 
         FIG. 20C  is an elevation view of a data-storage system  2002  of some embodiments of the invention that provides a high-density enclosure having one or more rows of disk drives with a cast-in-place vibration-damper boot  2076 . 
         FIG. 20D  is an elevation view of a data-storage system  2003  of some embodiments of the invention that provides a high-density enclosure having one or more rows of disk drives with a cast-in-place mid-drive vibration damper  2077 . 
         FIG. 21  is a front elevation view of a data-storage system  2100  of some embodiments of the invention that provides a high-density enclosure having one or more rows of disk drives with vertical beam stiffener  2110  and optional vibration damper  2122 . 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description of preferred embodiments, reference is made to the accompanying drawings that form a part hereof, and in which are shown, by way of illustration, specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention. The references to relative terms such as top, bottom, upper, lower, vertical, horizontal, etc., refer to an example orientation such as used in the Figures, and not necessarily an orientation used during fabrication or use. 
     Systems and methods to densely package disk drives in an enclosure, while at the same time reducing negative effects on the disk drives that are due to drive-to-drive interactions, can improve performance, density, reliability, and also reduce manufacturing costs and operational costs. 
     Individual disk drives include one or more head-disk assemblies (HDAs) and the electronics for control and data transfer to and from the disks. The HDA includes one or more disks and one or more actuator on which a head is attached. An actuator to which a head is attached is positioned within the disk drive such that the actuator can be rotated about an axis to selectively position the attached head to a select location on an adjoining disk. Accordingly, data can be retrieved from, or written to, a specific location on a disk by movement of the actuator to position the attached head at the specific location on the disk. 
     SYSTEM ENVIRONMENT: The present invention provides improved systems and methods to densely package the hard-disk drives in an enclosure, while at the same time reducing drive-to-drive vibration interaction. These can improve performance, density, reliability, and also reduce manufacturing and operational costs. Each hard-disk drive (HDD, also called “disk drive” or “drive”) includes one or more HDAs and the electronics for control and data transfer to and from the disks. 
     High-density packaging of HDDs in an enclosure exacerbates drive-to-drive vibration interaction problems. With several HDDs, packaged closely together in single enclosure, potentially many doing simultaneous head-seeks, the vibration interaction problem is greatly increased. Previous systems and methods to package HDDs and reduce drive-to-drive vibration interaction involved mechanical stiffening of the enclosure and/or lower density packaging options. 
     Hard-disk-drives are sensitive to vibration. The performance and reliability of a HDD are decreased with vibration. When multiple HDDs are operating within an enclosure, rotational-acceleration vibration generated from the head-seek operation on one HDD can adversely affect the read/write operations (and possibly head-seek operations as well) on other HDDs. (Note that non-acceleration vibration such as due to disk-spindle wobble, room noise, or fan vibration is generally less problematic than acceleration vibration due to actuator seek operations.) The drive-to-drive rotational-acceleration vibration interaction can cause the heads in an HDD to move off track, and thus cause read-data errors and write-data errors. Such errors may result in additional revolutions to re-locate the data, excessive retries, lost data, longer head-seek times, slow data access, increase power consumption and heat production. Reducing the vibration transferred between HDDs can improve HDD performance, density, reliability, manufacturing costs, and/or operational costs. 
       FIG. 1  is a perspective drawing of disk drive  120  mounted in a perpendicular-to-the-major-face orientation (e.g., vertical, if the major face is horizontal) in a disk-drive system  100 . In some embodiments, a plurality of other drives (up to one-hundred-fifty, one-hundred-ninety-two, two-hundred or two-thousand drives or more) are each plugged into their respective sockets (or to other suitable connectors) (e.g., connector  123 ) that are coupled to connector circuit  129  (e.g., in some embodiments, a plurality of insulated conductors carrying power and signals to and from drive  120 ) on connector circuit board or substrate  150 . Disk drive  120  includes one or more disks  115  that rotate around their axis  117 , an actuator  112  that rotates back and forth around its axis  111  to move its head  114  onto a given track  113  on disk  115 . The data is written serially on each track  113  (e.g., as magnetic domains in the case of magnetic recording disks, or as optical artifacts in the case of optical disks, or as atomic-force artifacts or other suitable information), so the head  114  must be moved to and kept on track  113  in order to read the data. Any movement of drive  120  that causes the drive  120  to have a rotational force  187  around its Z R120  center-of-mass axis, or a transitional rotation vibration force, can cause head  114  to be moved off track  113 . 
     Data is organized on the disk drive  120  in serial fashion. This means that the data is stored on individual tracks (e.g., track  113 ) on the disk  115 , which can be exemplified as concentric rings. A head that is positioned at a constant radius from the center of rotation of the disk is able to read data from a specific track on the disk as the disk turns. This allows data to be stored and retrieved from specific tracks on the disk by positioning the head above the specific track. However, if the position of the head is disrupted (i.e., moved off track), the head is no longer able to read the data from the desired specific track and must be repositioned. Accordingly, events that cause the position of the head to change in an undesired manner disallow proper reading of data from a disk and disallow proper writing of data to the disk. Examples of such events include shock to the disk drive, vibrational forces, torques, and the like. 
     The time required to find and transfer data on a disk is referred to as the access time. Access time can be divided into seek time, rotational latency, and data transfer time. Seek time refers to the time required to position an actuator on a track that contains the desired data. Rotational latency refers to the time required for the disk to spin such that the desired data on the requested track is under the head  114  of the properly positioned actuator  112 . Transfer time refers to the time required to transfer the data to or from the head  114  on the actuator  115  to a location on a track  113  where the data is stored or retrieved (put to use). The rate of data transfer can be altered by placing different portions of the data on different disk drives (this is called striping, explained further below). For example, data can be split into blocks that are stored on two or more disk drives. Different blocks of data can then be read from the multiple disk drives in an overlapped or parallel manner and used as needed without having to wait for a single disk drive to free up. This process allows overall data to be transferred more rapidly than if the data are stored on a single disk drive. The rate of data acquisition can also be altered by placing multiple copies of data onto a disk. For example, five copies of the same data block can be stored on a single track or closely adjacent tracks of a disk to reduce rotational latency as the disk would only have to turn at most one-fifth of a revolution for one of the copies of the data to be accessed (one tenth of a revolution on average), as compared to accessing data on average in one-half revolution for data that was stored on the disk as a single copy. (Since the location on the track where the head starts is random with respect to the location of the data, some of the time the head will reach the track exactly at a point in time that it can immediately access the data (no revolution time), and other times it will take a full revolution until the data is in a position to be accessed; thus, on average the rotational latency is generally a half revolution is a single copy of the data is used, and ½N revolutions if N copies of the data are stored.) Additionally, storing multiple copies of data on a single track can decrease the time required for data acquisition in the event of a tracking or other recoverable error, since the rotational latency would be reduced following repositioning of the head following the error. 
     When data is retrieved or written to a disk, a seek operation is used that rotates the actuator about its axis and positions the attached head at the track on the disk where the data is to be written or read. The rotation of the actuator arm produces a rotational force, wherein the disk drive experiences a rotational force in the opposite direction as the actuator motion. This rotational force can move the disk drive and thus move the neighboring enclosure and cause a neighboring drive to move. This can cause the track position of the actuator in that neighboring disk drive to change and if that disk drive is reading or writing data at the time, it will thereby cause a read or write error to occur in the neighboring drive. 
     In conventional disk-drive arrays, the enclosure and the HDA cases are quite heavy in relation to the mass of the actuator. Accordingly, the disk drives of the disk-drive arrays are less affected by rotational forces that are transferred from one disk drive doing a seek operation to a neighboring disk drive doing a read or write operation. As the mass of the HDA is reduced, the proportional mass of the actuator increases, and the relative rotational force due to the actuator is relatively larger. In addition, smaller drives allow the enclosure&#39;s metal case (which is used to fabricate the disk-drive-array enclosure) to be made thinner and less rigid. The resulting lighter weight can produce less damage to the unit if it is dropped. However, the thinner metal can also allow a greater amount of rotational or translational force to be transmitted between drives. Generally, moderate translational force is not a problem, nor is rotational force that does not move the read-write head (e.g., rotational acceleration around an axis perpendicular to the actuator axis). With increasingly smaller drives and thinner cases, the rotational force from a seek operation in one drive has a larger deleterious affect (i.e., primarily a rotational force that moves a head off track) that is transmitted to nearby disk drives and that results in the problems described. 
     Accordingly, these negative effects of rotational and translational force on disk drives are exacerbated by two major trends in the disk drive and disk array industries. The first of these is the trend toward smaller and lighter HDA mechanisms. As HDA mechanisms become smaller (as a function of disk diameter), the mass of platters decreases roughly as a function of the square of the platter radius. The mass of disk drive motors also tends to decrease exponentially as a function of disk diameter. However the mass of the head actuator tends to decrease only linearly, as a function of the length of the actuator. The result is that as HDA mechanisms become smaller, the mass of the actuator becomes a proportionately larger part of total HDA mass. The non-actuator portion of total HDA mass acts (beneficially) as an inertial mass (i.e., a damper of higher frequency vibrations since the heavier mass has a lower characteristic frequency) that attenuates rotational force, so the loss of non-actuator mass in proportion to total HDA mass represents a growing problem in disk arrays. 
     The second of these is the trend in disk arrays toward larger numbers of disk drives per unit of disk enclosure volume. Conventionally, these drives are lined up along the narrow front and/or back surface of the enclosure, where the right-angle corners constrain rotation and/or vibration. As disk drives are packaged more densely, they must be mounted interior to the enclosure on the membranes formed by the lower and/or upper covers, and the effect of inter-drive mechanical coupling and rotational and translational forces to nearby disk drives is exacerbated. With high-density enclosures and random disk accesses, the possibility of several HDDs generating additive rotational and/or translational forces is increased. In addition, the problem is greatly magnified for HDDs attempting to hold sector tracking while doing reads or writes. 
       FIG. 2  is a perspective view that illustrates a storage system  200 , according to some embodiments of the invention, with the disk drives placed in a new physical-layout pattern  250  that enables the disk drives  120 ,  120 ′, and disk-drive pairs  205 ,  206 ,  207 ,  208 ,  209 , (each having two disk drives  120 ) and the like, to individually and collectively serve as the “fins” of a large heat sink through which air is drawn or pushed in order to remove heat generated by the disk drives and the driving circuitry connected to use the disk drives. The arrangement of the disk drives further creates a plurality of tuned spaces such as inlet manifold  1112 , outlet manifold  1114  and between-drive spaces  95  that control air flow from fans  240  to a high degree of precision in order to increase cooling efficiency. In some embodiments, the staggered herringbone orientation of HDDs with graduated spacing between disk drives is to optimize cooling by forcing airflow between the disk drives and taking into account the increasing temperature of the air as it moves through the disk drives. Since heat transfer is proportional to the temperature difference between the air and the drives, and to the amount of air, more air is used where the air temperature is higher and the temperature difference is less. In some embodiments, system  200  is connected to one or more processors  89 , each coupled to communicated data to a plurality of disk-drive enclosure systems  201 ,  202 , and/or  203  and the like, each having a large plurality of disk drives  120 . In some embodiments, two or more power supplies  231 ,  232  provide redundant power for the disk drives  120 . In some embodiments, the fans  240  are locates at a far end of the airflow through the enclosure so they pull air through the disk drives and push the heated air out of the cabinet in order that the heat from the fans is inserted into the air stream after it has cooled the other components. In some embodiments, the fans  240  are accessible and possibly replaceable by the user or service persons at an exterior surface of the enclosure, but enough redundancy is provided for the disk drives and power so that the system can continue to operate with substantially full functionality even if multiple individual components fail. Thus, the disk drives can be held in place in the enclosure using visco-elastic adhesive along one or a few edges, reducing weight and virtually eliminating the need for service calls. Further, small DC-to-DC regulated power supplies can be permanently mounted (e.g., soldered, in order to reduce connector-caused failures) in place, since multiple ones of the power supplies can fail and yet the system continues to function fully using the remaining good power supplies. 
     Power-supply description:  FIG. 3A  shows a disk drive system  201  having a power supply  300 , as used in some embodiments of the invention. Power supply  300  includes a power crossover and power router configuration that meets the needs of a dense box of disk drives (DBOD). Power supply  231  includes two DC-to-DC power supplies  231 A and  231 B. 
     In some embodiments, each of these uses an AM80A-048L-050F40 model power supply available from Astec company. In some embodiments, the input to such a power supply includes dual 48-Volt DC supply lines with optional remote-control telecommunications to control the power. In some embodiments, the power modules can take DC input power from 36- to 72-Volt DC. One or more of the following features apply to some embodiments of the invention. The PRIMARY and MIRROR notation refers to drives that provide the primary data storage (the primary copy of data) and the mirrored data storage (the other copy or copies of the data). In some embodiments, there is no difference between primary and mirror copies of data, in that all write operations will write to all copies of the data, and read operations will only access one of the copies, wherein the selection of which copy is to be read is made on a rotation or alternating basis, or on a basis of which disk drive is not busy with another operation at the time when the read operation is started. For example, if the data are mirrored three ways, three disk drives will each have a copy of the same data, and when writing, the write data will be sent to all three disk drives, but when reading, a first read operation is sent to only the first disk drive, a second read operation is sent to only the second disk drive, and a third read operation is sent to only the third disk drive. When a fourth read operation arrives, it would generally be sent to the first disk drive, but if that disk drive is still busy with the first read operation, the fourth read operation could be sent to the second or third disk drive if either of those were finished with their earlier operations. By spreading the read operations among all the drives, it is more likely that a drive with the requested data for a particular read request will be available (that the data is on a drive that is not already busy with another prior operation). 
     In some embodiments, “Power Module Redundancy” is provided on the input, (i.e., each disk drive is configured to receive power from each of two or more DC-to-DC power supplies) wherein if any DC-to-DC power supply fails, it can be automatically disconnected and the remaining DC-to-DC power supply or supplies is able to handle the load. Like aircraft engines that have two spark plugs per cylinder, four cylinders, and “crossed over” ignitions for redundancy (e.g., two-way), some embodiments of the invention take a similar approach. In some embodiments, the sources 48V A and 48V B also cross the primary and mirrored boundaries. Dual redundant input (of the 48-volt DC sources) and the crossover configuration provide capability to power both sides in the event of a single 48V input loss. Each input can power both sides. In some embodiments, the power modules are made by Astec and provide less than 100-mV ripple (which is, in some embodiments, a requirement for the disk drives and some other power supplies cannot meet this), are parallelable, controllable, provide monitor sensors (e.g., voltage, temperature and current), provide high reliability that is more than one million hours MTBF (mean time between failures), regulatory approvals, and provide four voltage-range options: 18-36 VDC, 36-72 VDC, 90-200 VDC, and 180-400 VDC. This allows some embodiments to obtain power simply from AC, for example using a simple rectifier on the front end. In some embodiments, these power supplies provide an efficiency of 84 percent typical for 5 volts output, and ripple is 50 mV typical, and maximum 100 mV. In some embodiments, the entire box or enclosure of a plurality of drives is made to be “Hot Box” swappable (i.e., where an entire subsystem box is swapped out while the system is running), with just a little more switching to selectably disconnect power supplies  231  and  232  from their power sources. 
     In some embodiments, the next section or stage is the “power router.” This is a plurality of high-current, redundant relays (having a relatively low voltage drop at high current as compared to solid-state relays that have higher voltage drops) that can interconnect with each other, or switch power around, providing routing (if one should fail). When no power supply has failed, the switches connect a plurality of power supplies to each section of disk drives, thus reducing the amount of power that must be supplied by each power supply (e.g., in normal mode, each power supply provides half the power needed, and once a power supply fails, the other power supply provides all the power for its disk drives). 
     The last stage includes the disk drives. In some embodiments, each disk drive uses 5 volts DC, 5.5 Watts maximum (less than about one amp during power up). Lines drawn that “Link” the disk drives indicate which drives are mirrored, in some embodiments. This provides a data link between various copies of the mirrored data across different power sources 48-volt source A and 48-volt source B. In some embodiments, battery-backed uninterruptible power supplies (UPS) are provided for these sources. In some embodiments, Astec AM80A modules produce 240 Watts at 5-Volts DC, or 40 Amps at 5-Volts DC, for a 48-VDC input. In some embodiments, a version is used that is pin for pin compatible but more expensive, BM80A, 300 W, 60 A, if a design needs more power. 
     Some embodiments include four rows of forty-eight disk drives for a total of one-hundred-ninety-two drives. Rows are powered up one row at a time, sequentially over a period of time. When a row is powered on, the forty-eight disk drives may use 5.5 watts each maximum, just on power up, thus drawing 264 watts maximum for a short period of time. In some embodiments, two of the 240-Watt DC-to-DC power supplies are wired in parallel to provide this power requirement. Some embodiments provide additional individually activated relay switches, such that fewer disk drives (e.g., twenty-four at a time) are powered on at any one time. In some embodiments, two rows are powered on simultaneously, using different pairs of DC-to-DC power supplies. In some embodiments, a plot of disk-drive power over time at power up shows transient power to be below 0.5 amps after 3 seconds, but even if it is 10 or 15 seconds, or some other value; some embodiments provide a programmable delay between the power up of rows to keep the power draw well within the capability of the power supplies. 
     Sequencer timing and power control, in some embodiments, is simple, easy to develop and inexpensive. Some embodiments use one or more PIC-brand controllers (model PIC16F872, an 8-bit high-performance RISC CPU available from Microchip Technology Inc., Chandler, Ariz., is used for some embodiments) that are RISC-based CMOS technology and have an interface for chip-to-chip communication. In some embodiments, they provide temperature sensing and full environmental control. In some embodiments, the controller is made using one of the chip sets (such as model VSC7160 12-Port SAS Expander that can run at 1.5 Gbps and 3.0 Gbps, and that includes Table Routing and a Serial SCSI Protocol (SSP) engine, or model VSC7151 9-Port Serial Attached SCSI Edge Expander that can run at 1.5 Gbps and 3.0 Gbps) from Vitesse, or other suitable controller and/or expander chip sets for just-a-bunch-of-disks (JBOD) control. 
       FIG. 3B  is a schematic of a disk-drive data-storage apparatus  204  having a power supply  300 ′. In some embodiments, apparatus  204  includes a first circuit board  381  and a first plurality of disk-drive connectors  311  that are operatively coupled to the first circuit board  381 . The apparatus also includes a first plurality of electrically controlled relay switches  378  that include a first relay switch  320 , a second relay switch  322 , a third relay switch  326 , and a fourth relay switch  324 . The apparatus also includes a first plurality of DC-to-DC power supplies  374  that includes a first DC-to-DC power supply  312  and a second DC-to-DC power supply  314  that are operatively coupled to the first circuit board  381 . In some embodiments, the DC-to-DC power supplies  374  receive an intermediate power voltage. In some embodiments, the intermediate voltage is about 48 volts. In some embodiments, the plurality of DC-to-DC power supplies  374  are connected through the first plurality of switches  378  to supply power to each one of the first plurality of disk-drive connectors  311 . The plurality of DC-to-DC power supplies  374  provide crossover power to the plurality of switches  378  such that each one of the plurality of disk-drive connectors  311  is coupled through the plurality of switches  378  to each one of the first plurality of DC-to-DC power supplies  374 . Dual power inputs with crossover power being directed through the plurality of switches to a plurality of disk-drive connectors provide a redundant supply of power to the plurality of disk-drive connectors. 
     In some embodiments, sequencer  368  is operable to control a plurality of switches in order to sequentially power up subsets of a plurality of disk drives. Use of a sequencer reduces the magnitude of power surges occurring within the apparatus. For example, in some embodiments, the apparatus includes a sequencer  368  that is operable to control a plurality of switches  378  in order to sequentially power-up subsets  352  and  354  of the first plurality of disk-drive connectors  311 . In some embodiments, sequencer  368  first activates (e.g., applies power to the relay coils) only certain switches (e.g., switches  320  and  324 ) that supply power to one subset of the disk drives (e.g., subset  352 ), and at a slightly later time (e.g., 0.5 seconds to 5 seconds later, depending on the length of time that the disk drives draw extra power to spin up), sequencer  368  then activates only certain other switches (e.g., switches  322  and  326 ) that supply power to one other subset of the disk drives (e.g., subset  354 ). This reduces the maximum power surge that must be supplied by the power supplies  374  and  376  and by the AC-to-DC power sources  370  and  372 ). In some embodiments, sequencer  368  later activates only certain other switches (e.g., switches  328  and  332 ) that supply power to one other subset of the disk drives (e.g., subset  356 ), and still later sequencer  368  then activates only certain other switches (e.g., switches  330  and  334 ) that supply power to one other subset of the disk drives (e.g., subset  358 ). At four still later sequential times, sequencer  368  will successively activate the relay switches  336 - 350  to power on subgroups  360 ,  362 ,  364 , and  366 . By dividing the disk drives into subgroups (e.g., eight subgroups in the embodiment described above), the power surge for spin up is quite reduced. 
     In some embodiments, either individual power supply  312  or  314  alone can provide enough power for all of the disk-drive connectors to which it is operatively coupled. Accordingly, if a power supply  314  fails, the redundant power supply  312  is able to provide power to the plurality of disk-drive connectors and the apparatus will continue to operate. Power supplies that can be used within an apparatus of the invention can be obtained commercially (e.g., ASTEC POWER, Carlsbad, Calif. 92008). In some embodiments, each power supply will provide less than 100 mV of ripple. In some embodiments, each power supply will produce about 50 mV of ripple. Furthermore, power supplies having a variety of voltage-ranges may be used in various embodiments. In some embodiments, an AC power supply is used that has a simple rectifier and a voltage-range of, for example 18-36 VDC, 36-72 VDC, 90-200 VDC, 180-400 VDC, or the like. In some embodiments, each power supply within an apparatus is “Hot Box” swappable which enables the power supply to be removed and replaced while the apparatus is running. 
     In some embodiments, the apparatus includes one or more AC-to-DC power supplies or sources  370 ,  372  that are operable to receive AC wall power and to generate an intermediate power voltage. In some embodiments, an intermediate power voltage ranges from about 18 volts to about 36 volts. In some embodiments, an intermediate power voltage ranges from about 36 volts to about 72 volts. In some embodiments, an intermediate power voltage ranges from about 90 volts to about 200 volts. In some embodiments, the intermediate voltage is about 48 volts of direct current. 
     In some embodiments, the voltage output from a power supply into each one of the switches  320  to  350  is a voltage that is suitable to be used directly by a disk drive  120  that is plugged into one or more of the plurality of disk-drive connectors  126 . Examples of voltages that are suitable to be used directly by a disk drive include those within a range of 5 volts plus or minus five percent (e.g., for disk drives using the industry standard 2.5-inch form factor). In some embodiments, the suitable voltage is within a range of 3.3 volts plus or minus five percent (e.g., for disk drives using the industry standard 1.8-inch form factor). In some embodiments, the suitable voltage is some other suitable voltage selected for the disk drives used. 
     In some embodiments, a first switch  320  is connected to couple a first DC-to-DC power supply  312  to a first subgroup (proper subset)  352  of a first plurality of disk-drive connectors  311 , and the second switch  322  is connected to couple a second DC-to-DC power supply  314  to a second proper subset  354  of the first plurality of disk-drive connectors  311 . 
     In some embodiments, an apparatus includes a third switch  326  that is connected to couple a first DC-to-DC power supply  312  to the second proper subset  354  of the first plurality of disk-drive connectors  311 , and a fourth switch  324  that is connected to couple the second DC-to-DC power supply  314  to a first proper subset  352  of the first plurality of disk-drive connectors  311 . 
     In some embodiments, an apparatus includes a fifth switch  332  that is connected to couple the first DC-to-DC power supply  312  to a third proper subset  356  of the second plurality of disk-drive connectors  313 , a sixth switch  330  that is connected to couple the second DC-to-DC power supply  314  to a fourth proper subset  358  of the second plurality of disk-drive connectors  313 , a seventh switch  334  that is connected to couple the first DC-to-DC power supply  312  to the fourth proper subset  358  of the second plurality of disk-drive connectors  313 , and the eighth switch  328  is connected to couple the second DC-to-DC power supply  314  to a third proper subset  356  of the second plurality of disk-drive connectors  313 . 
     In some embodiments, an apparatus includes a third DC-to-DC power supply  316 . In some embodiments, an apparatus includes a fourth DC-to-DC power supply  318 . 
     In some embodiments, an apparatus includes a ninth switch  336  that is connected to couple a third DC-to-DC power supply  316  to a fifth proper subset  360  of a third plurality of disk-drive connectors  315 . In some embodiments, an apparatus includes a tenth switch that is connected to couple a fourth DC-to-DC power supply  318  to a sixth proper subset  362  of the third plurality of disk-drive connectors  315 . In some embodiments, an apparatus includes an eleventh switch  342  that is connected to couple a third DC-to-DC power supply  316  to a sixth proper subset  362  of a third plurality of disk-drive connectors  315 . In some embodiments, an apparatus includes a twelfth switch  340  that is connected to couple a fourth DC-to-DC power supply  318  to a fifth proper subset  360  of a third plurality of disk-drive connectors  315 . 
     In some embodiments, an apparatus includes a thirteenth switch  348  that is connected to couple a third DC-to-DC power supply  316  to a seventh proper subset  364  of a fourth plurality of disk-drive connectors  317 . In some embodiments, an apparatus includes a fourteenth switch  346  that is connected to couple a fourth DC-to-DC power supply  318  to an eighth proper subset  366  of a fourth plurality of disk-drive connectors  317 . In some embodiments, an apparatus includes a fifteenth switch  350  that is connected to couple a third DC-to-DC power supply  316  to an eighth proper subset  366  of a fourth plurality of disk-drive connectors  317 . In some embodiments, an apparatus includes a sixteenth switch  344  that is connected to couple a fourth DC-to-DC power supply  318  to a seventh proper subset  364  of a fourth plurality of disk-drive connectors  317 . 
     In some embodiments, the apparatus includes a sequencer  368  that is operatively coupled to each one of the plurality of switches  378 ,  380 ,  382 , and  384  and operable to apply power in a sequence over a period of time to the plurality of switches  378 ,  380 ,  382 , and  384  in order to reduce the magnitude of power-on surge. 
     In some embodiments, the apparatus includes a second circuit board  383  to which a second plurality of disk-drive connectors  313  are each operably coupled. In some embodiments, an apparatus includes a third DC-to-DC power supply  316  and a fourth DC-to-DC power supply  318  that are both operably coupled to a second circuit board  383 . 
     In some embodiments, the apparatus includes a plurality of disk drives connected to a first plurality of disk-drive connectors  311 . 
     In some embodiments, the apparatus is included within an enclosure. In some embodiments, the enclosure includes a first air-inlet manifold  1112  configured to direct air between a first plurality of disk drives and a first air-outlet manifold  1114  configured to receive warmed air and direct the warmed air out of the enclosure. 
     In some embodiments, an apparatus includes a multiprocessor having two or more processing units and a memory coupled to the processing units, wherein the memory is operable to send and receive data from a first plurality of disk drives. 
     In some embodiments, an apparatus includes a video-streaming subsystem, the video-streaming subsystem including one or more processing units and a memory coupled to the one or more processing units and operable to send and receive data from the first plurality of disk drives and to simultaneously output a plurality of video streams. 
     In some embodiments, an apparatus includes a video-on-demand controller operable to receive requests for video programming from each one of a plurality of users, and to access and direct video output to the plurality of users based on the requests. 
     In some embodiments, the invention provides a method that includes operatively coupling a first plurality of disk-drive connectors  311  to a first circuit board  381 , operatively coupling a first plurality of DC-to-DC power supplies  374  to the first circuit board  381 , and connecting the DC-to-DC power supplies  374  through a first plurality of electrically controlled relay switches  378  to supply power to each one of the first plurality of disk-drive connectors  311 . The plurality of power supplies  374  provide crossover power to the plurality of switches  378  such that each one of the plurality of disk-drive connectors  311  is coupled through the plurality of switches  378  to each one of the first plurality of DC-to-DC power supplies  374 . In some embodiments, the first plurality of electrically controlled relay switches  378  includes a first switch  320  and a second switch  322 . In some embodiments, the DC-to-DC power supplies  374  receive an intermediate power voltage. In some embodiments, the intermediate voltage is about 48 volts of direct current. In some embodiments, the first plurality of DC-to-DC power supplies  374  includes a first DC-to-DC power supply  312  and a second DC-to-DC power supply  314 . 
     In some embodiments, the method includes operatively coupling a sequencer  368  to control a first plurality of switches  378  in order to sequentially power up a first proper subset  352  and a second proper subset  354  of a first plurality of disk-drive connectors  311  over a period of time. 
     In some embodiments, the method includes providing an AC-to-DC power supply  370  that is operable to receive AC wall power and to generate an intermediate power voltage. 
     In some embodiments, the method includes providing an AC-to-DC power supply  370  having an intermediate voltage that is about 48 volts of direct current. In some embodiments, the voltage output from the AC-to-DC power supply  370  into each one of the switches  378  is a voltage suitable to be directly used by a disk drive that is plugged into one or more of the plurality of disk-drive connectors  311 . 
     In some embodiments, the method includes connecting a first switch  320  to couple a first DC-to-DC power supply  312  to a first proper subset  352  of a first plurality of disk-drive connectors  311 , and connecting a second switch  322  to couple a second DC-to-DC power supply  314  to a second proper subset  354  of a first plurality of disk-drive connectors  311 . In some embodiments, the method includes connecting a third switch  326  to couple a first DC-to-DC power supply  312  to a second proper subset  354  of a first plurality of disk-drive connectors  311 , and connecting a fourth switch  324  to couple a second DC-to-DC power supply  314  to a first proper subset  352  of a first plurality of disk-drive connectors  311 . 
     In some embodiments, the method includes connecting a fifth switch  332  to couple a first DC-to-DC power supply  312  to a third proper subset  356  of a second plurality of disk-drive connectors  313 . In some embodiments, the method includes connecting a sixth switch  330  to couple a second DC-to-DC power supply  314  to a fourth proper subset  358  of a second plurality of disk-drive connectors. In some embodiments, the method includes connecting a seventh switch  334  to couple a first DC-to-DC power supply  312  to a fourth proper subset  358  of a second plurality of disk-drive connectors  313 . In some embodiments, the method includes connecting an eighth switch  328  to couple a second DC-to-DC power supply  314  to a third proper subset  356  of a second plurality of disk-drive connectors  313 . 
     In some embodiments, the method includes connecting a ninth switch  336  to couple a third DC-to-DC power supply  316  to a fifth proper subset  360  of a third plurality of disk-drive connectors  315 . In some embodiments, the method includes connecting a tenth switch  338  to couple a fourth DC-to-DC power supply  318  to a sixth proper subset  362  of a third plurality of disk-drive connectors  315 . In some embodiments, the method includes connecting an eleventh switch  342  to couple a third DC-to-DC power supply  316  to a sixth proper subset  362  of a third plurality of disk-drive connectors  315 . In some embodiments, the method includes connecting a twelfth switch  340  to couple a fourth DC-to-DC power supply  318  to a fifth proper subset  360  of a third plurality of disk-drive connectors  315 . 
     In some embodiments, the method includes connecting a thirteenth switch  348  to couple a third DC-to-DC power supply  316  to a seventh proper subset  364  of a fourth plurality of disk-drive connectors  317 . In some embodiments, the method includes connecting a fourteenth switch  346  to couple a fourth DC-to-DC power supply  318  to an eighth proper subset  366  of a fourth plurality of disk-drive connectors  317 . In some embodiments, the method includes connecting a fifteenth switch  350  to couple a third DC-to-DC power supply  316  to an eighth proper subset  366  of a fourth plurality of disk-drive connectors  317 . In some embodiments, the method includes connecting a sixteenth switch  344  to couple a fourth DC-to-DC power supply  318  to a seventh proper subset  364  of a fourth plurality of disk-drive connectors  317 . 
     In some embodiments, the method includes operatively coupling a sequencer  368  to each one of a plurality of switches  378 ,  380 ,  382 , and  384  that are operable to apply power in a sequence over a period of time to the plurality of switches  378 ,  380 ,  382 , and  384  in order to reduce the magnitude of power-on surge. 
     In some embodiments, the method includes operably coupling a second plurality of disk-drive connectors  313  to a second circuit board  383 , and operably coupling a third DC-to-DC power supply  316  and a fourth DC-to-DC power supply  318  to the second circuit board  383 . 
     In some embodiments, the method includes including the apparatus  300  within an enclosure. In some embodiments, the enclosure forms a first air-inlet manifold  1112  configured to direct air between a first plurality of disk drives and a first air-outlet manifold  1114  configured to receive warmed air and direct the warmed air out of the enclosure. 
     In some embodiments, the method includes providing a multiprocessor that includes two or more processing units and a memory coupled to the processing units and that is operable to send and receive data from a first plurality of disk drives. 
     In some embodiments, the method includes providing a video-streaming subsystem that includes one or more processing units and a memory coupled to the one or more processing units that are operable to send and receive data from a first plurality of disk drives and to simultaneously output a plurality of video streams. 
     In some embodiments, the method includes providing a video-on-demand controller operable to receive requests for video programming from each one of a plurality of users, and to access and direct video output to the plurality of users based on the requests. 
       FIG. 3C  is a schematic of a disk-drive data-storage apparatus  204 ″ having a power supply  300 ″. In some embodiments, apparatus  204 ″ includes a first plurality of disk-drive connectors  311  that are operatively coupled to a circuit board. The apparatus also includes a first plurality of electrically controlled voltage regulators  312 ″- 314 ″ that are controlled by power-up sequencer  368  and connected to provide redundant sources of operating voltage to disk drives  120  in the subgroup of disk drives connected to connectors  311 . The apparatus also includes a second plurality of electrically controlled voltage regulators  316 ″- 318 ″ that are operatively coupled to provide redundant sources of operating voltage to disk drives  120  in subgroup  315 . In some embodiments, the electrically controlled voltage regulators  312 ″- 318 ″ receive DC power from one of a plurality of sources  388  of an intermediate power voltage. In some embodiments, the intermediate voltage is about forty-eight volts. 
       FIG. 4A  is a perspective drawing of disk drive  120  mounted in a perpendicular-to-the-major-face-of-the-enclosure orientation in a disk-drive system  400 . This disk drive  120  is as described for  FIG. 1  above. 
     In some embodiments (as shown in  FIG. 4A ), a second disk drive  120 ′ is mounted face-to-face, substantially parallel to, and adjacent to drive  120 , such that if simultaneous seek operations are performed to both drives from the same starting position and to the same ending track, the two rotational accelerations will at least partially cancel. With respect to drive  120 ′ and its Z R120′  center-of-mass axis (in some embodiments, Z R120′  is collinear with, and in the opposite direction as, Z R120 ), accelerations  147  around its Z R120′  center-of-mass axis are in the opposite direction (clockwise versus counterclockwise) and approximately equal in magnitude as accelerations  187  of drive  120 . 
     Rotational and translational forces that are produced by a disk drive can be transmitted to other disk drives. For example, if the front corner  119  (the corner furthest from actuator axis  111 ) is moved or rotated downward (as a result of torque  192 ) relative to the rest of the drive (and/or corner  121  is moved relatively upward), the actuator  112  will rotate in a direction  191  taking the head  114  off its track  113 . Conversely, if the actuator  112  rotates in a direction  191  for its seek operation, the front corner  119  moves downward  192  relative to the rest of the drive, transmitting rotational force to other drives in its neighborhood. Moving a head off track during a read or write operation causes a loss in performance, since an entire disk revolution is needed to get back to the data that was missed when the head moved off track. 
     Disk drives can be arranged through use of the methods of the invention to reduce transmission of rotational forces to neighboring disk drives. Additionally, the invention provides multiple disk drives that are arranged within an apparatus so that transmission of rotational forces from one disk drive to a neighboring disk drive is reduced. In some embodiments of the invention, a second drive  120 ′ is placed back-to-back to drive  120 , such that its disks  145  are rotating in the opposite direction as disks  115 , and its actuator  142  moves in the opposite direction around its axis  141  as does actuator  112  relative to an outside frame of reference. In some embodiments, connector  116  of drive  120  is plugged into socket  126  on board  150 , and is held by one or more visco-elastomeric (or, in some embodiments, elastomeric, rubbery, soft plastic or otherwise compliant to some degree) holder(s)  127  and  128 . Similarly, connector  156  of drive  120 ′ is plugged into socket  166  on board  150 , and is held by one or more visco-elastomeric (or, in some embodiments, elastomeric) holder(s)  167 . In some embodiments, drives  120  and  120 ′ are mounted so that their Z R  center-of-mass axes are aligned, and actuators  112  and  142  are driven with substantially simultaneous operations, in order to cancel some or all of the rotational forces due to their respective seek operations. 
     In contrast to rotational forces, an up or down movement of board  150  at location  118  directly under the drive&#39;s center of rotational mass will merely cause a translation motion in the Y T  direction  182 , which does not cause a rotation around the Z R  center-of-mass axis, and thus does not cause tracking errors in drive  120 . Thus, a rotational force received at point  118  causes fewer problems than if at corner  119  or corner  121  of drive  120 . Further, if the actuator  112  moves in a direction  191  for its seek operation, the point  118  does not move upward or downward, but experiences a minor twist, transmitting very little rotational force to other drives if their corner  119  is closest to this point  118  on drive  120 . Thus, very little rotational force is transmitted from point  118 ; this causes fewer problems to neighboring drives if their corner  119  or corner  121  is closest to this point  118 . 
     Translational displacements  180  which move the entire drive  120  in X T  direction  181 , Y T  direction  182 , or Z R  direction  183  generally do not cause tracking errors, nor does rotational acceleration  185  around the X R  center-of-mass axis or rotational acceleration  186  around the Y R  center-of-mass axis. However, a rotational acceleration  187  around its Z R  center-of-mass axis is problematic, as described above. 
     Disk drives are generally able to function adequately in environments that induce/transmit translational vibrations along 3 axes of the drive (translational movements along X T , Y T  and Z T  will not move the head off track, since the actuator is generally quite balanced on its rotational axis) and angular acceleration or rotational force about 2 axes (X R , Y R ; see  FIG. 4A ) also do not generally move the head off track. However, rotational force that is transmitted to the head-disk assembly (HDA) around the Z R -axis is problematic. Rotation of the actuator around this axis is what moves the head that is attached to the actuator from track-to-track. When caused by the actuator motor, this moves the head to the desired track during a seek operation. However, when its neighboring drives transmit rotational force to a drive, sector-tracking problems can occur. Even a very small amount of rotational force is known to increase the position-error signal of the head, cause instability in the servo system, degrade I/O performance, increase power consumption and increase error rates of disk drives. During any seek operation, an HDA using a rotary head actuator generates rotational force in a direction opposite to that of the acceleration of the head actuator, and transmits this energy to the environment around it, including other disk drives. Disk drives are most sensitive to rotational force during the sector-tracking media transfer phase of operation, but are less sensitive to rotational force during a seek operation. 
     The following aspects and embodiments of the invention are aimed at reducing the effects of rotational and translational forces among a plurality of disk drives mounted in a mechanical enclosure. In addition, where RAID hardware or software logic is used to increase the performance and/or reliability of a plurality of disk drives, the following aspects and embodiments also describe how the disk drives can be arranged mechanically in relation to one another and in relation to RAID striping and mirroring logic to reduce the effects of rotational and/or translational forces. 
     Embodiment A1 
     Counter-Rotating Disk Drives in a Mirrored Set to Offset Rotational Acceleration Vibration (RAV) 
     “Mirrored disks” are a set of M (where M is two or greater) disk drives that are logically connected as a set and at least some of the data written to that logical set is replicated to each of the M drives for each write operation. In some embodiments, all data sent to the set of drives is replicated, while in other embodiments, some amount (e.g., one-hundred-fifty GB) or some percentage of the drive&#39;s data space (e.g., fifty percent) is mirrored and the remaining data on each drive is unique or different, in order to provide mirrored speed and redundancy for the portion that is replicated, while also providing a lower cost per gigabyte for the other data by writing only a single copy. The processor elements (PEs) or operating system (OS), in some embodiments, could see a set of four three-hundred-GB drives as one four-way-mirrored drive of one-hundred-fifty GB, plus four non-mirrored drives of one-hundred-fifty GB each. In some embodiments, some portion or percentage of the data is replicated with a higher number of copies (e.g., a set of four three-hundred-GB drives could have thirty percent of the data or 90 GB replicated four times, once for each disk drive, with the operating system software seeing one 4-way-mirrored ninety-GB drive), while other data is replicated across fewer drives (e.g., ninety GB replicated twice to a first pair of drives, and another 90 GB replicated twice to a second pair of drives, so the OS sees two 2-way-mirrored ninety-GB drives), and/or split differently (e.g., one-hundred-twenty GB replicated thrice to three drives, and another one-hundred-twenty GB sent as non-mirrored data to a fourth drive, so the OS sees one 3-way-mirrored 120-GB drive and one non-mirrored one-hundred-twenty-GB drive). In such mirrored embodiments, every full-mirrored write operation is sent to all N drives, so every drive has a copy of all the data, while subset-mirrored writes are sent only to the specified subset. In some embodiments, each of a plurality of subsets of the drives have drives placed alternately back-to-back or front-to-front, as shown in  FIG. 4A , so that half of the drives are rotating in the opposite direction as the other half. In some embodiments, read operations are also sent to all N drives (or to all of the subset of drives having the replicated data), so the drive that can return the data fastest has its data used, and the other drives&#39; data is discarded. This provides the increased reliability of the duplicated data, and increases read performance to that of the drive that happens to have the least rotational latency (by the happy chance of having the rotational angle of its disks closest to the requested data) to reach the requested data. Further, since all seek operations (reads and writes) are sent to all M drives (or subset of M drives) of the set at substantially at the same time, the rotational accelerations of the M simultaneous seek operations cancel, at least to some extent. Further there are no seek operations for some of the drives while others of this set of M drives are reading or writing, tracking errors due to RAV are reduced. 
     Embodiment A2 
     Counter-Rotating Disk Drives in a Mirrored Set to at Least Partially Offset RAV, Optionally Also Using Read Splitting 
     Again, every write operation is sent to all M drives, so every drive has a copy of all the data. In some embodiments, each read operation is sent to only one of the M drives, so the other drives have less utilization and can accept read operations to retrieve other data. This provides the increased reliability of the duplicated data, and increases read performance since more drives can be performing separate read operations simultaneously. Again, the drives are placed alternately back-to-back or front-to-front, as shown in  FIG. 4A , so that half of the drives are rotating in the opposite direction as the other half. Since all write seek operations (only for writes) are sent to all M drives of the set, the rotational accelerations of the write-seek operations cancel, at least to some extent. Further, to the extent that probability allows, the read-seek operation to one drive will not occur during the read-data-tracking portion of a read to another drive of the set of M drives. Since all drives have the same data, four successive read commands to any of the data can each be sent to a different drive. 
     In some embodiments, read operations to large blocks of data are broken into smaller read commands, each to a different portion of the data, and each sent substantially simultaneously to a different drive of the set. Thus, if M=4, a read operation to fetch, for example, a 640-KB block of data is broken into four 160-KB read operations, each sent substantially at the same time to a different drive of the set. Thus, four seeks of substantially the same duration and to approximately the same locations on each drive will occur at about the same time. Two would have a clockwise acceleration and the other two would be counter-clockwise. The first drive would return the first 160-KB portion of the 640 KB-read request, the second drive would return the second 160-KB portion, the third drive would return the third 160-KB portion, and the fourth drive would return the fourth 160-KB portion. This provides the advantage of the counter-rotating seek commands canceling some of the RAV, the seek operations occurring when the other drives are not trying to keep on track and not occurring when heads are trying to stay on track, and the speed of parallel data retrieval providing improved performance. 
     Some embodiments use vulnerability mapping, described below, as one basis for selecting which drive or drives are to be used for a read-split read (i.e., a read operation that could be satisfied by data stored on any one of a mirrored set of drives since all prior write operations replicated their data on all drives of that mirrored set). 
     Embodiment A3 
     Counter-Rotating Disk Alternation in a Striped Set to Offset RAV 
     “Striped disks” are a set of N disk drives that are logically connected as a set and data written to that logical set is spread across the set. At some level of granularity, a block of data is broken into sub-blocks, wherein each successive sub-block is written to a different drive. Thus, the block need not wait to be entirely written to or read from one drive in a serial manner, but instead the set of drives works in parallel, each writing or reading their portion of the block. The set of striped disks are, or can be, viewed by the system&#39;s processors as a single logical disk drive having a capacity that is the sum of the capacities of all drives in the set, and wherein each successive block of data (where a block can be any convenient size, such as 512 bytes, 8192 bytes, or any other desired size) is written to a different drive (with a plurality of N drives, every Nth block is written to the first drive, every N+1 st  block is written to the second drive, and so on). When data is written to or read from the logical disk that includes the set of striped physical disk drives, a single I/O request to the logical disk frequently spans two or more logically adjacent physical disk drives (each having one stripe of the data), and as a result, there is a high probability of simultaneous actuator-seek movements among these neighboring head-disk assemblies (HDAs). 
     In some embodiments, the minimum processor-level block size is made to be an N multiple of the minimum drive-level block size, such that every processor-level read or write is automatically striped across N drives of a set. For example, if N=4 and the processor-level block size is made 8 KB, the drive-level block size is made 2 KB, and each read operation from the processor causes a read operation to each one of the N drives. An 8-KB processor read causes four 2-KB read operations, while a 16-KB processor read causes four 4-KB read operations, one to each of the drives of the set. A 56-KB write operation causes four 14-KB write operations, one to each of the drives of the set. The N operations, one to each one of the N drives in a set will be to the same logical address on each drive, and thus cause substantially simultaneous seek accelerations that cancel if the drives are alternately clockwise and counterclockwise. Since the N operations that are sent to the N drives each access 1/N of the data, the data-transfer phase is shortened. Often, the seek accelerations are rotational accelerations that tend to be substantially simultaneous, and similar in duration, speed/acceleration, direction and frequency in the N drives of a set. By alternating the position (face-to-face or back-to-back) of each of the drives in the stripe, the combined rotational accelerations of the HDAs will, by design, offset one another other as shown in  FIG. 4A . In some embodiments, for example, a 16-KB read operation from the system is broken into two 8-KB operations to logically adjacent drives in a set, where a first drive has a seek in a clockwise direction as seen from its top cover, and a second drive also has a seek in a clockwise direction as seen from its top cover, but when the top covers are face-to-face adjacent, these two rotational accelerations are in opposite rotational directions and at least partially cancel each other&#39;s mechanical motions. Coupling disk drives in this way, both mechanically and also to the RAID striping logic, takes advantage of the simultaneity of seek operations, during which time the disk drives are largely insensitive to RAV disturbances. 
     In some embodiments, it also takes advantage of the local stiffness of board  150  between two adjacent HDD connectors. That is, in some embodiments, the connectors themselves provide stiffening, and in some embodiments, the connectors are molded in pairs such that they are more rigid to one another. In some embodiments, such a pair of unitary-molded connectors is attached to the bottom metal plate using a visco-elastic material that dampens any vibrations that otherwise would be transferred to the bottom metal cover, and the more rigid connection between the two connectors allows the counter-rotating accelerations to cancel. In some embodiments, more than two drives are alternately placed face-to-face, then back-to-back, then face-to-face, etc., and more than two of the drives will have simultaneous seek operations (e.g., two clockwise drives and two counter-clockwise drives). 
     In other embodiments, a pair of drives has one of its drives write data from the inner diameter to the outer, and the other drive writes its data from the outer diameter to the inner. Such a pair can be placed both facing the same direction (i.e., face-to-back) such that when one does a seek operation from the inner-to-outer diameter, the other will have a seek operation from the outer-to-inner (the opposite rotational direction), and their total rotational acceleration will at least to some extent cancel. These embodiments, however, have non-symmetrical seeks at the outer or inner diameters (when one drive seeks at its outer diameter, the other drive of that pair seeks at its inner diameter), since a seek operation that moves across, for example, 20-GB of data has fewer tracks to move at the outer diameter than at the inner diameter. 
     In other embodiments, each pair of drives includes one drive that rotates its disks and actuator in the opposite rotational direction as those in the other drive. This requires non-standard drives (i.e., half of the drives are built as mirror-images as viewed from the cover), but allows all the drives to be facing in the same direction (i.e., face-to-back). These embodiments, however, have symmetrical seeks at the outer or inner diameters, since a seek operation done at the outer diameter of one drive, will be accompanied by a seek operation in the opposite direction but also at the outer diameter or the other drive. 
     Thus, some embodiments have one or more pairs of disk drives, each pair operated such that their actuators are operated substantially simultaneously. This provides the advantage that the counter-rotating rotational accelerations, at least to some extent, cancel one another. This canceling reduces the RAV transmitted to other drives near the pair in the enclosure, as well as reducing the RAV within the pair. It also provides the advantage, that even if not performed exactly at the same time, each acceleration (due to an actuator seek) occurs when the neighboring drive is also in or temporally near the seek mode time, and thus is less susceptible to read or write errors than if the rotational acceleration occurred while that drive&#39;s head was on track and trying to write or read. 
     In addition, since the system sends down a set of one or more system-sized blocks, and the set of N drives (where N can be two or more drives) each write a disk-sized blocks, each being the system block size divided by N, the data can be written twice as fast, once the drives reach the desired data location (i.e., after the seek and rotational delay). Suppose the system has a granularity of 8192 bytes (commonly called 8-KB blocks), and the drives are organized as 2-KB blocks (2048 bytes), then a pair of drives can write the first and third 2-KB blocks to the first drive of a pair, and the second and fourth 2K the second drive. Alternatively, a “pair” could include two physical pairs, or four drives, each receiving a 2-KB portion of each 8-KB write operation. In other embodiments, other numbers of drives can be used in each set of drives. 
     In other embodiments, a replicated set of drives can be provided, wherein data is M-way mirrored and N-way striped. For example, fifteen disk drives can be configured as a 4-way-mirror, 5-way-stripe set of drives (e.g., if 200-GB drives are used, five groups of four mirrored drives each form a one-terabyte logical drive, where each block of data is replicated four times, and data is striped across the five groups of mirrored drives). In such embodiments, the mirrored drives can be configured to have counter-rotating pairs or quads to cancel at least some of their RAV. When mirroring is done with an even number of replications (i.e., M=2, 4, 6, etc.), all write operations can be RAV balanced (the same number of seek commands being sent to clockwise-rotating (CW) drives as to counterclockwise-rotating (CCW) drives). 
     For systems performing read splitting and if a read command specifies data kept on an odd number of drives, or for write operations if M and N are both odd numbers (e.g., M=3 and N=5), approximately half of the drives can be configured to rotate in the opposite direction as the other approximately half (e.g., 7 CW and 8 CCW drives). Commands sent to such a configuration have almost all of the RAV of the set of drives cancelled by almost balancing (for all but one drive) the clockwise (CW) acceleration with counterclockwise (CCW) acceleration. 
     In other embodiments, an exactly even number of counter-rotating seek operations can be sent, even if the data requested (to be read or written) is kept on an odd number of drives, by sending one unused seek operation to another drive of a set—for example to a spare drive (i.e., one with no system data stored on it, but which is provided in order to be able to swap for a failed drive in the future, if and when a failure occurs or is predicted) or to an idle drive (i.e., one that has system data on it) (e.g., if 3-way mirroring and 5-way striping were used, and one spare drive was provided for the other 15 drives, for each access that accessed an odd number of drives (e.g., 3, 9 or 15 drives), a seek to the spare drive would also be simultaneously sent, but for accesses that accessed an even number of drives (e.g., 6 of 12 drives), no seek command would be sent to the spare drive. In this way, counter-rotating seeks to the drives would always substantially cancel the rotational acceleration. 
     Embodiment B 
     Orthogonal Placement of Disk Drives as Rotational-Force Mass Dampers 
     When data is read from or written to a plurality of mechanically coupled disk drives, each seek operation issued to any disk produces a corresponding rotational force in the head-disk assembly (HDA) mechanism, the energy of which is transmitted to surrounding structures which either absorb or transmit that energy. When a subject disk absorbs an RAV component produced by another nearby disk about the Z R  axis of the subject disk, the negative effects of RAV are maximized. By positioning a plurality of disk drives orthogonally to each other, the RAV energy created by one drive may be transmitted to and absorbed by the mass of nearby orthogonally oriented drives without acting on the subject drives around their Z R  axis, which is the axis of greatest sensitivity. 
       FIG. 4B  shows a pair of drives in a T orientation. Neighboring disk drive  160  is at a right angle (at or about ninety degrees) to reference drive  120 , with its corner  119  placed nearest to point  118  (under the center of rotational mass) of drive  120 , then drive  120  acts as an inertial mass that resists the rotational force motion  192 ′ from the neighboring drive  160 , and drive  120  suffers little or no tracking errors, since the neighboring drive&#39;s rotational force  192 ′ acts as a Y T  translational movement, not a rotational force for drive  120 . Conversely, any rotational force  192  of drive  120  causes the least motion at point  118  of drive  120 , and thus does not cause rotational tracking errors in the neighboring drive  160 . The moments of inertia of the drives will be about axes that are orthogonal to each other. This allows the mass of orthogonally positioned disk drives to act as a mass damper for rotational force produced by nearby disk drives and allows rotational force to be dissipated harmlessly around the X-axis and Y-axis of subject disk drives, which is an advantageous situation for either reading or writing of data. A rotational force  187  of drive  120  around its Z R120  axis causes little or no movement at point  118 , and thus causes no tracking error in drive  160 . A rotational force  188  of drive  160  around its Z R160  axis causes only translational movement at point  118  of drive  120 , and thus causes no tracking error in drive  120 . 
       FIG. 4C  shows a pair of drives in a Y orientation. Neighboring disk drive  159  is at an oblique angle to drive  120 , with its corner  119  placed nearest to point  118  (under the center of rotational mass) of drive  120 , then drive  120  acts as an inertial mass (as in  FIG. 4B ) that resists the RAV motion from the neighboring drive  159 , and drive  120  suffers little or no tracking errors, since the neighboring drive&#39;s motion acts as a Y T  translational movement, not a rotational force. In some embodiments, the Z R159  axis of drive  159  aligns with the back corner  121  of drive  120  (Z R159  axis passes next to the rear edge of drive  120 ). By having the perpendicular plane containing the Z R159  axis also include the rear edge of drive  120 , then point  118  of drive  159  is closer to rear corner  121  of drive  120  than is either of corner  119  or corner  121  of drive  159 . 
       FIG. 4D  shows a pair of drives in a counter-rotating parallel orientation with their axes of rotation aligned. That is, Z R120  axis of reference drive  120  is co-linear with Z R161  axis of neighboring drive  161 . In some embodiments, seek operations are synchronized (by pairing, striping or both), such that rotation force  187  of drive  120  is to some extent simultaneous with and cancels some or all of rotational force  466  of drive  161 . In some embodiments, each pair of drives  120  and  161  is mounted in a shuttle or holder  170  that holds the drives at the necessary offset  171  to align rotational axis Z R161  to rotational axis Z R120 , and to provide a convenient carrying, electrical, and/or cooling holder that can be easily inserted into the disk-array enclosure. In some embodiments, such a holder  170  is provided for other sets of two or more drives (such as for  FIG. 4A ,  4 B,  4 C,  4 E, or  4 F), to make handling easier. 
     Thus, in some embodiments, the invention provides one or more drive holders or cages  170  for holding a plurality of counter-rotating disk drives (e.g., drive  120  and drive  161 ). In some embodiments, each holder  170  holds two drives, one drive rotating in a clockwise direction and the other rotating counterclockwise. In other embodiments, each holder  170  holds more than two drives, where half of the drives are rotating in a clockwise direction and the other half rotating counterclockwise. In some embodiments, each holder  170  includes a single connector to connect to board  150 , and a plurality of connections, one to each of the contained drives. In some embodiments, each holder  170  includes air-flow openings and one or more air-deflection vanes  175  to help direct the airflow through the drives in the enclosure. In some embodiments, each holder  170  is substantially only a wire-frame following an outline of the drives, wherein the drives are held in place by one or more visco-elastic or elastomeric bands  173 , or are adhesively affixed to wire-frame holder  170 . 
       FIG. 4E  shows a pair of disk drives (reference drive  120  and neighboring drive  162 ) in a counter-rotating parallel orientation with each of their edges  119  aligned to edge  121  of the other drive. Even though (at least for drives whose centers of rotational mass do not coincide with the X-direction centerline of the drive) the center of rotational mass axis Z R162  of drive  162  will not exactly align with the center of rotational mass axis Z R120 , at least some of the rotational force will cancel if the seek operations overlap completely or to some extent. 
       FIG. 4F  shows a pair of drives in a counter-rotating parallel orientation each with its axis of rotation aligned with an edge of the other drive. In this configuration, rather than trying to cancel the clockwise and counterclockwise rotational forces, the corner  121  of a reference (first) drive  120  is placed next to the center-of-rotational-mass point  118  of the neighboring (second) drive  163  (rotational axis Z R120  of drive  120  is aligned to the edge of neighboring drive  163 ), and the corner  121  of the second drive  163  is placed next to the center-of-rotational-mass point  118  of the first drive  120  (rotational axis Z R163  of neighboring drive  163  is aligned to the edge of drive  120 ). In other embodiments, corners  119  of each drive are aligned next to point  118  of the other drive. Thus, either one of these two drives can perform a seek while the other is trying to read or write, and transfer little or no rotational force to the other drive. In some embodiments, drive  120  is front-to-front facing drive  163 , as shown. In other embodiments, drive  120  is front-to-back to drive  163  (the front of both drives facing the same direction. In some embodiments, offset  172  is selected to align corner  121  of each drive to the center-of-rotational mass  118  of the other drive. 
     Furthermore, the angle alpha (see  FIG. 4C ) between the two drives may be a function of the structural environment (transmission path) that connects the two drives. The mass, stiffness, shape and properties of the connecting structure will offer a “tunable” platform to minimize rotational force effects between drives in a paired and/or rowed set. The angle of offset could vary depending on the structure, and may range from 90 degrees (where the drives are perpendicular) to 0 degrees (where the drives are parallel, and, in some embodiments, the parallel drives are offset in the X direction). In some embodiments, the placement of drives is based, at least in part, on a computer simulation of the expected vibration-transmission and/or standing-wave resonance patterns. In other embodiments, a mock-up is built with movable masses that represent the masses of the disk drives (e.g., actual disk drives are used, in some embodiments), and the masses are iteratively moved, tested, moved again, and tested again, etc., until a satisfactory resonance pattern is achieved that also provides a suitable air-flow pattern for cooling. 
       FIG. 4G  shows a herringbone configuration  400  with counter-rotating pairs of drives, e.g.,  410 ,  411 ,  412 ,  413 , and  414  that are in T-orientations to one another, e.g.,  420 ,  421 , and  422 . Note that in the T-orientation set  421  that counter-rotating pair  413  has its center of rotation  430  aligned to the corner  440  of pair  410  that move the most on a seek, and also to corner  444  of drive pair  414 . This provides cross-wise stiffening at these corners  440  and  444 , while also exposing the least sensitive area  430  (i.e., if the center of rotation (COR) is moved up or down, there is much less likelihood of error than if this area is rotated) of drive pair  413 . 
       FIG. 5  shows, for some embodiments, a herringbone T configuration  500  with counter-rotating pairs of drives. The drives  548  at the downstream end of a heating air flow are spaced further apart than are the drives at the upstream end. Further, the center area  550  is left open so the source of cooling air has better access to the drives deep in the enclosure. 
       FIG. 6A  shows another herringbone configuration  600  with counter-rotating pairs of drives, not in a T-orientation, but in a parallel configuration that places a corner  640  of a first pair of drives  601  closest to the COR  612  if a second pair of drives  602 , and the corner  641  of drive pair  602  next to the COR  611  of drive pair  601 . This pattern is repeated for pairs  603 ,  604 ,  605 ,  606 , and  607 , and in the series of pairs to the right etc. Notice also that the rearward or upward end drives  605 ,  606 , and  607  are spaced further from one another than are the frontward or lower drives  601 ,  602 , and  603 . In some embodiments, the fans are omitted and the  692  end of the enclosure is uppermost and the  691  end is lowermost (e.g., of a vertically-aligned enclosure), in order that heat convention pulls air up through the enclosure, allowing cooling with fewer or no fans. In other embodiments, the enclosure is mounted horizontally, with ends  691  and  692  substantially horizontally aligned with one another, and fans providing the air movement. In some embodiments, air “turbulators”  695  are provided, particularly for the wider spaced, in order to introduce turbulence and have more of the cooling air come into contact with the drive pairs  605 - 607 . 
       FIG. 6B  is a schematic plan view of the configuration of an enclosure  601  having a plurality of approximately right-angled paired disk-drive connectors  629 . In some embodiments, each individual one of the disk-drive connectors  129  of the first plurality of disk-drive connectors  650  and each corresponding respective one of the disk-drive connectors  129 ′ of the second plurality of disk-drive connectors  651  are oriented so that each pair of connectors form about a ninety-degree angle. In some embodiments, each pair  629  has a first connector  129  for a first disk drive  120  and a second connector  129 ′ for a second disk drive  120 ′, where a corner of the first disk-drive connector  129  is near a corner of the second disk-drive connector  129 ′ and the two connectors are oriented at an approximately ninety-degree angle to each other. In some embodiments, a first plurality of disk-drive connectors  129  are coupled electrically and mechanically to a substrate  150  in a first row  650  and a second plurality of disk-drive connectors  129 ′ are coupled to the substrate  150  in an adjacent second row  651  that is substantially a mirror image of the first row  650 . In some embodiments, a disk-drive connector  129  in the first plurality of disk-drive connectors  650  and a second disk-drive connector  129 ′ in the second plurality of disk-drive connectors  651 ′ are oriented such that a disk drive  120  connected to the first disk-drive connector  129  produces a rotational force at the adjacent corner  670  (e.g., downward into substrate  150  for a particular seek direction and magnitude) that is opposite that produced by a second disk drive  120  that is connected to the second disk-drive connector  129 ′ at the adjacent corner  671  (e.g., up out of substrate or board  150  for a particular seek direction and magnitude). In some embodiments, data is striped across the disk drives  660  that are connected to the first plurality of disk-drive connectors  650  and the same data is mirrored to and striped at corresponding locations (e.g., logical-block addresses, or LBAs) across the disk drives that are connected to the second plurality of disk-drive connectors  661 . In some embodiments, data that is striped on disk drives  660  that are connected to the first plurality of disk-drive connectors  650  is mirrored onto corresponding respective ones of the plurality  661  of disk drives  120  that are connected to the second plurality of disk-drive connectors in row  651 , such that rotational force resulting from a read or write function in the first plurality of disk drives is opposed by the rotational force resulting from the same read or write function in the second plurality of disk drives. In some embodiments, inlet air dams  618  at the air inlet side force air  113  into the inlet manifolds  1112 , then between the drives and outlet air  115  is drawn by fans  696  out the outlet side (e.g., rear) of enclosure, and outlet air dams  616  form the rest of the airflow guidance. In some embodiments, circuit board  150  is made in two or more (e.g., horizontal) parts  1512  and  1514  that connect to a single (e.g., vertical) circuit board that is connected to both connectors  513  and  515 , and provides wiring to either a controller card mounted parallel to board  150  at the opposite end of drives  120 , or to cables running out the rear of the enclosure (e.g., at the top of  FIG. 6B ). 
       FIG. 7A  shows a plan view of yet another herringbone configuration  700  with alternating counter-rotating pairs of drives  701 ,  702 ,  703 ,  704 . The drives at the top or back  692  of the enclosure  692  are spaced further apart than are the drives near the bottom or front  691 . In some embodiments, the controller board  694  is mounted on edge between the covers to stiffen them and provide vibration isolation. In some embodiments, a display  1695  (either one-sided or two-sided) is mounted to stick out at a right (or other suitable) angle from the front or bottom of the enclosure, so as not to interfere with air flow through the fans  696 , while providing easy viewing at an angle for a user in front of the unit. 
       FIG. 7B  shows an abstraction perspective view of storage subsystem  700  of  FIG. 7A . 
       FIG. 8A  is a front perspective drawing of prior-art “high-density” hard-disk-drive (HDD) enclosure systems  81  and  82  as might be mounted in a rack  80 . In some embodiments, enclosure system  81  is 3 U or 5.25 inches high (13.34 cm), while in others enclosure system  82  is 2 U or 3.5 inches high (8.89 cm). In some embodiments, enclosure system  81  contains a plurality of disk drive enclosures  91 , whereas in other embodiments enclosure system  82  contains a plurality of drive enclosures  92 . 
       FIG. 8B  is a front perspective drawing of a high-density HDD enclosure system  810  according to the present invention. In some embodiments, this enclosure is 4 U high or 7 inches (17.78 cm), and contains the plurality of disk drives  120 , each drive  120  coupled to the enclosure  892  via one or more connectors  110 . In some embodiments, a plurality of drives  120  is aligned in one or more substantially straight rows  850 . 
       FIG. 8C  is a top-down perspective drawing of a high-density HDD enclosure system  811  using a “herringbone” configuration according to the present invention. This herringbone configuration contains the plurality of disk drive enclosures  92 , separated by one or more tuned air-flow spaces such as inlet manifold  1112 , outlet manifold  1114  and between-drive spaces  95 . In some embodiments, system  811  contains one or more fan  696  for allowing air to flow into the system  811 , and one or more of these fans  696  for urging air to flow out of the system  811 . 
       FIG. 8D  is a front perspective view that illustrates a system  812  having a perforated support grid  819  for a plurality of disk drives  120  with an anti-ESD-coated (i.e., having a high-resistivity (but not insulating) coating for electro-static discharge prevention and/or dissipation) visco-elastomeric material, and height-adjustment screws  820 . 
       FIG. 8E  is a top view that illustrates a system  813 , which, in some embodiments, includes a set of nesting support grids  818  (for a plurality of disk drives  120 ) made with ESD-(electro-static discharge prevention)-coated visco-elastomeric material. In some embodiments, each support grid  818  fits over a pin  817  and provides a plurality of spaced-apart connection points  821  to each drive  120 . 
       FIG. 8F  is a front perspective view that illustrates system  814 , which, in some embodiments, has a separate molded-in ESD-coated visco-elastomeric material connector support (mold-in connector support)  846  for each one of a plurality of drives  120  mounted in a vertical orientation. In some embodiments, each of the drives  120  has a notch  844  to independently secure each of the drives  120  in the mold-in connector support  846 . This notch  844  locks into a detent  845  in support  846 . Each of the drives  120  connects to a circuit board via a connector  126 . 
       FIG. 8G  is a top view of system  814  of  FIG. 8F  that, in some embodiments, contains a plurality of the illustrated drive  120  each secured in its molded-in connector support  846 . 
       FIG. 8H  is a top view that illustrates the top view of a high-density HDD enclosure system  815  using a herringbone configuration according to the present invention, wherein, in some embodiments, there is a distribution of temperature sensors  851  around the tuned airflow spaces such as inlet manifold  1112 , outlet manifold  1114  and between-drive spaces  95 . This herringbone configuration contains the plurality of disk drives  120 , separated by one or more tuned airflow spaces such as inlet manifold  1112 , outlet manifold  1114  and between-drive spaces  95 . In some embodiments, system  815  contains one or more fans  240  for allowing air to flow into the system  815 , and one or more of these fans  240  for allowing air to flow out of the system  815 . 
       FIG. 8I  is a front view that illustrates a status display grid system  816 , wherein, in some embodiments, the display grid system is composed of various light emitting diodes (LED). Specifically, in some embodiments a green LED  861  is used by itself or in combination with a yellow LED  862  and/or a red LED  863 . And again, in some embodiments the yellow LED is used by itself of in combination with the green LED  861  and/or the red LED  863 . In still further embodiments the red LED  863  is used by itself or in combination with the green LED  861  and/or the yellow LED  862 . 
       FIG. 8J  is a perspective view that illustrates an exposed front view of a system  817  wherein, in some embodiments, a cover-latching mechanism is used to seat the drives into their connectors. In some embodiments, this cover-latching mechanism is contained in a case  852  which is 4 U high or 7 inches (17.78 cm), and is placed into a 19 inch (48.26 cm) rack unit. In some embodiments, contained within this case  852  is a plurality of drives  120 , which can be seated or unseated using a cam  872  mechanism movably attached to a handle  871 . The handle  871  is used to lift or lower the cam  872  and to seat or unseat the plurality of drives  120 . When the plurality of drives  120  are seated, the cam  872  sits recessed in a slot  873 . In some embodiments, individual drives  120  may be seated or unseated using the above disclosed cover-latching mechanism. 
       FIG. 9A  is a perspective view of a system  900  that illustrates a porous display  910  having LEDs  911  mounted on a screen  912  that has much space for air flow  920  through the display. In some embodiments, the display  910  includes a plurality of different color LEDs (e.g., red, green, blue, and/or yellow) that can be activated by control unit  915  that senses various parameters in system  900  (such as temperature, air flow, disk-drive status, performance (e.g., input-output operations per second, or IOPS, and the like), and generates appropriate text and/or graphical display messages that are transmitted to the array  910  of LEDs  911  for viewing by a user or operator. In some embodiments, a connector  919  is provided to connect controller unit  915  to the display  910 . By attaching the LEDs to a sparse grid having conducting wires therein, air flow is improved since the air can flow through the display rather than being forced around the display. In some embodiments, a grid is provided having openings that are approximately 6 mm by 6 mm passing through a grid having grid support (e.g., wiring and insulating supports) that is about 1 mm or less in diameter. 
       FIG. 9B  is a perspective view of a system  901  that illustrates one or more LCD displays  930 ,  931  mounted on the inlet air dams  918  allowing much space for air flow  920  around the displays  930  and  931 . The configurations of displays  930  and  931  provide an alternative to the configuration of flow-through display  910  of  FIG. 9A . In some embodiments, a circuit board  1500  has a plurality of disk-drive connectors  1923 , each of which connects to its respective disk drive  120 . In some embodiments, the disk drives  120  are mounted to the top side of board  1500 , and one or more DC-to-DC power supplies  1866  are attached to the bottom of board  1500 . In some embodiments, a plurality of cross-brace members  941  and  942  are provided between bottom cover  1979  and circuit board  1500  to provide stiffness. In some embodiments, a center circuit board  966  (in some embodiments, board  966  includes one or more metal I-beams in parallel with it for further stiffness—see  FIG. 21 ). In some embodiments, a controller unit  953  includes a controller circuit board  960  that includes a plurality of serial expander circuits  1663 ,  1665 , and a top sheet metal cover  961 . In some embodiments, enclosure  950  includes a bottom enclosure  952  that provides an air manifold for power supply  1866 , a middle enclosure  951  that provides air manifolds  1112  and  1114  directing air around disk drives  120  and a top enclosure  953  directing air around controller card  960 . In some embodiments, center board  966  is pulled into a socket on board  1500 , and, in turn, provides a plug-and-socket connection  964 ,  965  to controller board  960 . In some embodiments, expander circuits  1663 ,  1665 , are distributed among top-controller card  960 , middle connector board  966 , and disk-drive connector board  1500 . In some embodiments, disk drives are arranged in pairs  120 ,  120 ′ that are oriented and operated to counteract rotational vibration, as described elsewhere herein. In some embodiments, fans  1615  mounted on the rear of system  901  pull air  920  through the system between the drives  120 , across the circuit boards  1500 ,  966 , and  960  and around the power supplies  1866 . The air is exhausted through outlet ports  1202  and the rear of the unit. 
       FIG. 9C  is a front elevation view of system  901  that illustrates LCD displays  930 ,  931  mounted to the inlet air dams allowing much space for air flow around the displays and between the drives  120 . The other reference numbers indicate features and configurations of the corresponding units shown in  FIG. 9B  and described above. 
       FIG. 10  is an illustration of a system  1000  wherein, in some embodiments, one or more multiple-disk-drive units  901  are operatively coupled to one or more multi-processors (MPs)  1002 , of supercomputer  1005  and/or one or more video-streaming unit  1003 . In some embodiments, each MP  1002  includes memory  1009  and two or more processing elements (PEs)  1008 . In some embodiments, supercomputer  1005  is a high performance scientific computer well known in the art. In some embodiments, supercomputer  1005  is connected to an internet  50 . Video-streaming units  1003 , in some embodiments, provide the capability for video-on-demand to a large plurality of subscribers such as homes  55  connected to cable system  56 , in order to provide each subscriber with a selectable source of television programming. 
     In some embodiments, the invention includes a computer-readable medium  51  (such as a diskette, CDROM, FLASH ROM with a USB plug, internet-connected data source, or the like) having control information (such as, for example, instructions, tables, formulae, state transitions, data structures, and/or the like) stored thereon for causing a suitable programmed apparatus, such as system  1000  or other system described herein, to execute one or more of the methods described herein. For example, in some embodiments, supercomputer  1005  and/or video-streaming units  1003  of  FIG. 10  provides a programmable information processor that is coupled to read and obtain control information (such as instructions and/or data structures) from computer-readable medium  51  (which can include storage that is accessed across internet  50 ), and coupled to control apparatus  1000  or other system described herein, according to the instructions stored on the medium. 
       FIG. 11  is a plan-view block diagram of a data-storage system  1100  of some embodiments of the invention that provides a high density enclosure that, in some embodiments, has one or more rows  1150  of disk drives  120  (only one row  1150  is shown in  FIG. 11 ). In some embodiments, system  1100  includes an enclosure  1110  that holds a plurality of disk drives  120  in a straight row  1150 . Other embodiments provide a plurality of such rows. In some embodiments, enclosure  1110  is fabricated from sheet metal. In other embodiments, the enclosure is fabricated from other materials that include plastic, fiberglass, reinforced composites, and the like. In some embodiments, enclosure  1110  is made to a standard form factor such as a five-unit (or 5 U, referring to a height) enclosure for a nineteen-inch (48.26 centimeter) rack. (A rack unit or “U” is an Electronic Industries Alliance (EIA) standard unit for measuring the height of rack-mount-type equipment. One rack unit is one-and-three-fourths inches (1.75 inches) (about 4.45 cm) in height. A 5 U enclosure is eight-and-three-fourths inches (8.75 inches) (about 22.23 cm) high. Enclosure  1110  has a first surface  1138  facing the air inlet side  1101  (the side having inlet port  1109 , which is typically called the “front”) and an opposite second surface  1136  facing the air outlet side  1102  (the side having exit port  1119 , which is typically called the “back”). In some embodiments, side  1101  also includes one or more user-input buttons and/or a status display for showing the status of the enclosure as a whole, performance numbers, the status of one, several, or all the enclosed disk drives, and the like. 
     In some embodiments, a plurality of systems  1100  (e.g., two rows, three rows, four rows, or any other number of rows  1150 ) are enclosed side by side in a single enclosure sharing a common first surface  1138  and second surface  1136 . In some embodiments, a first face  1121  of each disk drive is facing one direction along the axis of row  1150  and the opposing second face  1122  is facing the opposite direction along row  1150 . For example, in some embodiments, the first face  1121  includes a metal cover  1123  that covers the disks and actuator and opposite side (second face  1122 ) includes a printed circuit card  1124  that holds the electronics for the disk drive  120 . Along one side of disk-drive row  1150  is air-inlet manifold  1112  that conveys inlet air  1113  to one edge of the disk-drives  120  in row  1150 . In some embodiments, the plan cross-section shape of inlet manifold  1112  is rectangular, and the plan cross-section shape of outlet manifold  1114  is also rectangular in shape. Thus, each of the disk drives is aligned along a straight line perpendicular to the “front” first surface  1138  and to back second surface  1136 . In some embodiments, a visual display panel is mounted on surface  1138  to show information messages and/or the status of each individual disk drive  120 . Along the opposing side of disk-drive row  1150  is air-outlet manifold  1114  that conveys outlet air  1115  from the opposite edge of the disk-drives  120  in row  1150 . In some embodiments of the apparatus  1100 , the inlet air manifold  1112  has a length  1141  measured parallel to the first row that is longer than the inlet air manifold&#39;s width  1142  measured perpendicular to the first row  1150 , and wherein the outlet air manifold  1114  has a length measured parallel to the first row that is longer than the outlet air manifold&#39;s width measured perpendicular to the first row  1150 . 
     In some embodiments, enclosure  1110  is oriented vertically such that the cool inlet air is induced upwards within air-inlet manifold  1112 , then the cross-face air  1111  flows between each adjacent drive in horizontal direction and is heated, the warm outlet air  1115  rises by convection to the exit port  1119  of air-outlet manifold  1114 . This convection helps pull additional inlet air into the system  1100 . In some other embodiments, a fan is provided to provide increased air flow. In some such embodiments, the fan is positioned at the exit port  1119  of air-outlet manifold  1114  in order that its self-generated heat (e.g., about 2 watts for each fan, in some embodiments) is inserted into the airstream as it exits the enclosure, after the air has passed across the disk drives, thus improving the disk-drive heat-transfer characteristics of system  1100 . 
     In some embodiments, the spacings  1126  between disk drives increase in relation to their position in row  1150  from the inlet side (the bottom of  FIG. 11 ) to the outlet side (the top of  FIG. 11 ), in order that an equal amount of cooling is provided to each of the disk drives. For example, some embodiments provide a relatively small spacing  1125  between disk drives  120  near the air inlet side  1101  and a relatively larger spacing  1127  between disk drives  120  near the air outlet side  1102 . In some embodiments, the same small spacing  1125  is used for each of the disk drives near the air inlet side  1101  and the same larger spacing  1127  is used for each of the disk drives near the air outlet  1102  and, intermediate spacing is used for disk drives between. In some other embodiments, a gradually increasing spacing is used (e.g., following an exponential curve) in which the spacing follows the exponential curve with an increase in spacing occurring toward the air outlet side  1102 . 
     In some embodiments, the air flow speed and turbulence creates a standing wave of variable pressure and the spacings between individual pairs of the disk drives are empirically determined or varied (other embodiments use computer analysis of the air flow to adjust the spacings) to compensate for the standing wave and provide more even cooling for each disk drive  120 . In some embodiments, the amount of airflow decreases in relation to the distance from the air inlet and thus the spacing between the drives is increased in order to achieve an equivalent amount of air cooling for each disk drive  120 . At the air inlet side, a blocking panel  1118  provides an enclosed airspace at the bottom face (the face closest to the bottom of  FIG. 11 , which depending on the orientation of the enclosure  1110 , may or may not be downward facing in the installed system  1100 ) of the first disk drive  120  in row  1150 . A corresponding blocking panel  1116  provides an enclosed air space at the top face (the face closest to the top of  FIG. 11 , which depending on the orientation of the enclosure  1110 , may or may not be upward facing in the installed system  1100 ) of the last disk drive  120 . 
       FIG. 12  is a plan view block diagram of a data-storage system  1200  of some embodiments of the invention that uses tapered inlet and outlet air chambers. System  1200  holds a plurality of disk drives  120  in a straight row  1250  that is oriented in a non-perpendicular acute angle relative to first surface  1238 . System  1200  has a first surface  1238  facing the air inlet side  1201  and an opposite second surface  1236  facing the air outlet side  1202 . In some embodiments, a plurality of systems  1200  (e.g., two rows, three rows, four rows, or any other number of rows  1250 ) are enclosed side by side in a single enclosure sharing a common first surface  1238  and second surface  1236 . In some embodiments, a first face  1121  of each disk drive is facing one direction along the axis of row  1150  and the opposing second face  1122  is facing the opposite direction along row  1250 . Along one side of disk-drive row  1250  is air-inlet manifold  1212  that conveys inlet air  1113  to one edge of the disk-drives  120  in row  1250 . In some embodiments, the plan cross-section shape of inlet manifold  1212  is substantially triangular, and the plan cross-section shape of air-outlet manifold  1214  is also substantially triangular in shape. In some embodiments, a visual display panel (not shown), such as an LCD dot matrix display with backlighting or an LED dot-matrix display, is mounted on front surface of triangle-shaped air blocking structure  1218  in order to be able to show information messages and/or the status of each individual disk drive  120 . Note that due to the triangular shape of inlet manifold  1212  and the diagonal orientation of row  1250 , a much larger (in some embodiments, about twice the area) air inlet port  1201  is provided compared to air inlet port  1101  of  FIG. 11 . Thus the display area on the front of blocking structure  1218  is smaller. Along the opposing side of disk-drive row  1250  is air-outlet manifold  1214  that conveys outlet air  1115  from the opposite edge of the disk-drives  120  in row  1250 . 
     In some embodiments, system  1200  is oriented vertically such that the cool inlet air  1113  is induced upwards from inlet port  1209  within air-inlet manifold  1212 , then the cross-face air  1111  flows between each adjacent drive in an upward-angled direction and is heated, the warm outlet air  1115  rises by convection to the exit port  1219  of air-outlet manifold  1214 . This convection helps pull additional inlet air into the system  1200 . In some other embodiments, a fan is provided to provide increased air flow. In some such embodiments, one or more fans are positioned at the exit port  1219  of air-outlet manifold  1214  in order that its self-generated heat (e.g., about 2 watts for each fan, in some embodiments) is inserted into the airstream as it exits the enclosure, after the air has passed across the disk drives, thus improving the disk-drive heat-transfer characteristics of system  1200 . Because of the diagonal orientation of the drive, a larger area is available for installation of fans or other air-movement devices. 
     In some embodiments, the spacings between disk drives  120  increase in relation to their position in row  1250  as described above for  FIG. 11 . Other aspects of disk drive spacing described for  FIG. 11  also apply to some embodiments of system  1200 . 
     At the air inlet side  1201 , a substantially triangular blocking structure  1218  provides an enclosed airspace at the bottom face (the face closest to the bottom of  FIG. 12 , which depending on the orientation of the system  1200 , may or may not be downward facing in the installed system  1200 ) of the first disk drive  120  in row  1250 . A corresponding blocking structure  1216  provides an enclosed air space at the face of disk drive  120  closest to the top of  FIG. 12 . 
     In some embodiments of apparatus  1200 , the inlet air manifold  1212  has a length  1141  measured parallel to the first row that is longer than the inlet air manifold&#39;s width  1142  measured perpendicular to the first row  1250 , and wherein the outlet air manifold  1214  has a length measured parallel to the first row that is longer than the outlet air manifold&#39;s width measured perpendicular to the first row  1250 . In some embodiments of apparatus  1200 , the inlet air manifold  1212  has a length  1241  measured perpendicular to air inlet side  1201  that is longer than the inlet air manifold&#39;s width  1242  measured parallel to air inlet side  1201 , and wherein the outlet air manifold  1214  has a length measured perpendicular to air outlet side  1202  that is longer than the outlet air manifold&#39;s width measured parallel to air outlet side  1202 . In some embodiments, one or more of these conditions also applies to the apparatus shown in  FIG. 13 ,  FIG. 14 ,  FIG. 16A ,  FIG. 17 ,  FIG. 18 , and other systems described herein. 
       FIG. 13  is a plan view block diagram of a data-storage system  1300  of some embodiments of the invention that uses curving tapered inlet and outlet air chambers. System  1300  holds a plurality of disk drives  120  in a curved row  1350  that is oriented relative to first surface  1338 . System  1300  has a first surface  1338  facing the air inlet side and an opposite second surface  1336  facing the air outlet side. Along one side of disk-drive row  1350  is a curved substantially triangular shaped air-inlet manifold  1312  that conforms to the shape of the curve of row  1350 . In some embodiments, the plan cross-section shape of outlet manifold  1314  is curved to conform to the opposite curved side of row  1350 . In some embodiments, the curve of row  1350  substantially follows an exponential curve, in order to provide more even air flow between each of the adjacent disk drives. Other aspects of system  1300  are as described above for  FIG. 11  and  FIG. 12 . 
       FIG. 14  is a plan view block diagram of a data-storage system  1400  of some embodiments of the invention that uses curving tapered inlet and outlet air chambers, and laterally offset paired drives. System  1400  holds a plurality of disk drives  120  in a curved row  1450  that is oriented at an angle relative to first surface  1438 , however, the disk drives are arranged in coupled pairs  1430 , each pair having a disk drive  120  facing generally towards air inlet side  1438  and another disk drive  120  facing in an opposite direction (generally towards air outlet side  1436 ). For example, a first disk drive  120  can have its metal face  1121 ′ facing the exit side  1436  and its printed circuit side  1122  facing inlet side  1438 , while the other drive of the coupled pair  1120 ′ has its metal face  1121 ′ facing inlet side  1438  and its printed circuit side  1122 ′ facing outlet side  1436 . Thus each coupled pair  1430  includes a disk drive  120  having disks that rotate in a first direction (for example, clockwise) and another disk drive  120  having disks that rotate in an opposite direction (for example, counterclockwise). More important than the direction of disk rotation, in some embodiments, is the direction of rotational acceleration due to actuator seek operations. This is because disk rotation assumes a steady-state velocity (no acceleration due to disk rotation), however actuator seek operations cause rotational acceleration that can be transmitted as a vibration to neighboring disk drives. This rotational acceleration vibration can force a transducer off its desired track during a read or write operation thus causing an error and a retry or recovery operation which slows the system and hinders performance. 
     Some embodiments mirror data across a two (or more) drives that are physically across from one another in adjacent rows of disk drives. In some embodiments, the data is mirrored across a pair of (i.e., two) disk drives, wherein each write access writes the same data to the same (corresponding) addresses in each respective disk drive, and wherein each read access is sent to only one drive (either alternating between the two drives, or sent to the drive that is idle at the moment). By alternating or spreading the read accesses so a read is sent to only one disk drive of a set, the disk drives are less busy and more available to quickly access the requested data. In some embodiments, the mirrored pair are physically oriented to be perpendicular to one another, or at a non-parallel angle, in order to provide additional stiffness and vibration resistance. 
     Some embodiments stripe data across multiple disk drives in a row. In some embodiments, this is done in addition to mirroring as just described. In some embodiments, the system&#39;s address space is divided into a plurality of stripes, and each stripe is multiple sectors (e.g., using a plurality of adjacent logical block addresses) located on one disk drive, and successive stripes are located on different disk drives. For example, in some embodiments, each stripe is the same size (e.g., 32 sectors/16 KB, 64 sectors/32 KB, 128 sectors/64 KB, 256 sectors/128 KB, 512 sectors/256 KB, 1024 sectors/512 KB, 2048 sectors/1 MB, or other suitable sizes). 
     Some embodiments “fork” data across two or more drives. Forking data across disk drives is similar to striping data across drives, except that the minimum size of a data access (a read or write operation) by the system (e.g., one kilobyte, in some embodiments using two disk drives, or two KB in embodiments using four disk drives) is an integer multiple of the minimum size of a data access (a read or write operation) allowed by each drive (e.g., one-half kilobyte, in some embodiments). In some embodiments, every read access and every write access to a forked set of drives causes all drives of the forked set to perform the same access (i.e., since the same access is sent to the same address on each drive, all drives will start and end on the same track as the other drives. This reduces the number of independent arms, but increases the data transfer rate while keeping the seek and rotational latency the same. Further, if a pair of forked drives is physically oriented so that the rotational accelerations at least partially cancel because of the simultaneous seeks; this can reduce tracking errors and improve performance for some workloads. For example, in some embodiments, the even numbered sector addresses would be sent to one disk drive of a mechanically coupled pair, and the odd numbered sector addresses would be sent to the other disk drive of the pair. Data transfer times are thus substantially reduced, especially for long data lengths. By forking the data evenly across a pair of disk drives  120  such that half of every data block is on the clockwise rotation disk drive and the other half of the respective data blocks is on the counterclockwise rotation disk drive, every rotational acceleration seek operation to the first disk drive will be accompanied by an equal and opposite rotational acceleration seek operation to the second disk drive. By forcing these rotational accelerations to be simultaneous, some or all of the rotational acceleration will be counteracted or cancelled. In some embodiments, the rotational acceleration due to actuator seek operations is minimized by sending simultaneous seek commands to each drive of a coupled pair  430 . This reduces error rates and increases system performance. Further, because two drives are providing the data, some aspects of data-transfer bandwidth can be doubled. In some embodiments, the axis of rotational mass  1440  of each disk drive  1120  within a coupled pair  1430  is aligned to be collinear (lying on or passing through the same straight line or having axes lying end to end along a straight line) with the axis of rotational mass of the other disk drive  120  of that coupled pair  1430 . In some embodiments, one or more disk drives  1432  is not a member of a coupled pair. For example, if an odd number of operating drives is provided, or if one or more drives fails, it is sometimes not possible for all drives to be members of respective coupled pairs. In some embodiments, spare drives are provided in coupled pairs such that if one drive of one of the operating sets of coupled pairs fails, the spare pair can be substituted for the coupled pair having the failed drive. In some embodiments, at a later time, it may be desirable to use the now-single remaining operational drive of the swapped-out pair to be used in some capacity, (e.g., if all the spare pairs are used up, a single drive failure could cause swap of the now-single remaining operational drive for the newly failed drive). Other aspects of system  1400  are as described for  FIG. 11 ,  FIG. 12 , and/or  FIG. 13 . 
       FIG. 15  is a plan view block diagram of a disk-drive-connector circuit card system  1500  used in some embodiments of the invention. In some embodiments, a rear circuit card  1512  has a relatively short center aspect such that its connector  1513  is closer to the top of circuit card system  1500  (as illustrated in  FIG. 15 ) and circuit card  1514  has a relatively longer center aspect such that its connector  1515  is also closer to the top of circuit card system  1500  (as illustrated in  FIG. 15 ). By having connector  1515  closer to the top of the circuit card system  1500 , a shorter perpendicular connector card can be used to connect connectors  1515  and  1513  to the top of the circuit card system  1500  (in some embodiments, this is the back of the enclosure which includes the air outlet side of the enclosure). In some embodiments, gap  1520 , between circuit card  1514  and circuit card  1512 , matches the angle of the space between disk-drive connectors at its edges  1522 ,  1524 ,  1526 , and  1528 . Thus, gap  1528  is at an angle to the front of the enclosure that matches the angle of the disk drives in that respective row. Accordingly, the gap  1528  between circuit cards  1512  and  1514  falls midway between two neighboring disk-drive connectors. Thus the continuity of disk drive spacing within a row is not interrupted. This allows the connectors that are adjacent to these edges to be completely on either circuit card  1512  in the case of a connector on one side of gap  1520  or on circuit card  1514  in the case of the connector adjacent the other side of gap  1520 . The pattern of gap  1520  further allows an at least approximately equal number of disk drives to be placed on circuit card  1512  as are placed on circuit card  1514  while still mounting connector  1515  closer to the top of circuit card system  1500 . By splitting the connector circuit onto two cards, the longest dimension of each card is reduced, making manufacturing easier and less expensive, and increasing yields. In some embodiments, the length of circuit card system  1500  is approximately 32 inches (about 81.28 cm), and the width is about 17 inches (about 43.18 cm), however each of the cards  1512  and  1514  have a length and width each less than about 20 inches (50.8 cm) making fabrication easier and less costly than if longer dimensions are used. 
     In some embodiments, redundant power supplies are provided for each circuit-card portion. For example, in some embodiments, two DC-to-DC power supplies, either of which could alone supply sufficient power for about fifty disk drives, are provided and connected to one side of each circuit board  1512  and  1514  (e.g., the bottom side, in some embodiments), and about fifty disk-drive sockets are provided and connected to the opposite side of each circuit board  1512  and  1514  (e.g., the top side, in some embodiments). In some embodiments, DC-to-DC power supplies that use forty-eight volts input, and that supply one or more output voltage and current values, as required by the disk drives, are used. In other embodiments, three such DC-to-DC power supplies, any two of which could supply sufficient power for about fifty disk drives, are provided for each circuit-board portion  1512  and  1514 . In still other embodiments, other power-supply configurations are used. High-reliability relays of the type used in automotive applications and having almost no internal voltage drop across the relay contacts (unlike solid-state relays which typically dissipate a not-insubstantial amount of power) are used, in some embodiments, to selectively connect the power supplies to the disk drives when desired or disconnect them if a failure is detected. In some embodiments, these relays are used to sequentially connect a few drives at a time upon power-up, in order to reduce the power surge due to spin-up of the disks. 
       FIG. 16A  is a plan view block diagram of a data-storage system  1600  of some embodiments of the invention that provides a high-density enclosure having (in this exemplary embodiment) four rows of disk drives. In some embodiments, system  1600  is mounted (e.g., in a rack) with its major faces horizontal, the front side with air inlet ports  1201  being at the bottom of  FIG. 16A , the back side with air outlet ports  1202  at the top of  FIG. 16A , and with the left and right sides of enclosure  1610  being closed. Inlet air  1113  is guided toward the back or top of inlet manifold  1212 , and a little of this air splits off between each pair of drives  120  to cool the disk drives, and the warmed outlet air  1115  collects in outlet manifold  1214  and is drawn by fans  1615  through and out outlet ports  1202 . In some embodiments, the disk drives themselves act as heat-sink fins (e.g., of the enclosure as a whole, as well as for the electronic circuits on circuit boards  1512  and  1514  and the disk drives themselves), both directing air flow and conducting heat into the air flow passing though the spaces between the disk drives. Reference numbers in  FIG. 16  that are not explicitly described here refer to elements discussed previously and shown in earlier Figures. 
     Each row  1650  has a plurality of drives (in some embodiments, up to fifty or more disk drives  120 ). Front wedges  1618  provide air passages in front of the front-most disk drives, and back wedges  1616  provide the same function for the rear-most disk drives, thus assuring that each and every disk drive receives the appropriate amount of air flow on both sides of every drive. In some embodiments, blank spacers are placed at socket positions that do not have disk drives in order that air flow is not disrupted by blank openings where disk drives are missing (air flow going through the path of least resistance). 
     In some embodiments, a centrally mounted personality board  1660  is plugged into socket or connector  1515  of the front circuit board  1514  and into socket or connector  1513  of the rear circuit board  1512 . 
       FIG. 16B  is a functional block diagram of a circuit  1608  used in some embodiments of system  1600 . In some embodiments, a plurality of M first-level fanout-fanin expander circuits  1664  are each connected to a plurality of disk drives  120  (e.g., each circuit provides N=six, eight, ten, twelve, or some other number of “downward busses”  1668  to a like number of disk drives) and each fanout-fanin expander circuit  1664  provides one or two intermediate “upward busses” including upward bus  1666  onto which is placed the consolidated data traffic to and from the N drives (e.g., a first upward bus onto which system data is sent or received, and a second upward bus that remains in the enclosure for status, data reconstruction, and display purposes). In some embodiments, the second upward bus  1663  from each of the first-level fanout-fanin circuits are fed directly, or through further fanout-fanin concentrator circuits that feed into, a status controller or maintenance computer  1669  in the enclosure, which tracks status of all the drives, and if a drive has failed or has been detected to be in a condition that indicates the drive is about to fail, the data from that drive is reconstructed (for example, the data is copied from a drive that mirrors the data on the failed drive) and placed on a spare drive, that from then on is used in place of the failed drive. In some embodiments, status controller  1669  also provides a driver to display various messages on display  930  as described for  FIG. 9A ,  FIG. 9B , and  FIG. 10 . 
     In some embodiments, the first M upward busses  1666  are in turn consolidated through further fanout-fanin expander circuits  1665  to a fewer K number of upward externally-presented data busses  1661 . In some embodiments, personality board  1660  includes electronic circuits that provide some or all of the circuitry for presenting upwardly a plurality of serial attached SCSI (SAS) busses (e.g., about ten to about twenty-five busses, in some embodiments, providing connectivity to about two-hundred disk drives), or alternatively, provide a plurality of serial ATA busses (e.g., about ten to about twenty-five busses, in some embodiments). 
     As shown in  FIG. 16C , in some embodiments, each of these serial external busses  1661  is connected to its own electronic fanout-fanin circuit  1672  that connects either directly to a plurality of disk drives (e.g., one or two external busses on one side of the circuit and eight, ten, or twelve disk drives each connected to its bus  1666  on the other side of circuit  1672 , in some embodiments), or connects to further levels of fanout-fanin circuitry as shown in  FIG. 16B . 
     Referring again to  FIG. 16A , in some embodiments, the split line (the demarcation)  1520  between the plurality of boards is made such that all connectors for disk drives  120  or connectors for personality board  1660  are completely on one board (e.g.,  1512 ) or another (e.g.,  1514 ). In some embodiments, a first plurality of on-board DC-to-DC power supplies (e.g., three power supplies, in some embodiments) is connected to board  1512  and selectively switched to provide redundant power to the plurality of disk drives that are connected to board  1512 , and a second plurality of on-board DC-to-DC power supplies (e.g., three power supplies, in some embodiments) is connected to board  1514  and selectively switched to provide redundant power to the plurality of disk drives that are connected to board  1514 . In some embodiments, a set of sequentially activated switches (e.g., solenoid-controlled relays) on each board are connected from the various power supplies to different subgroups of disk-drive connectors, in order to reduce the magnitude of surge current that is drawn by the disk drives as they spin-up. 
       FIG. 17  is a plan view block diagram of a data-storage system  1700  of some embodiments of the invention that provides a high density enclosure having one or more rows of disk drives accommodating a variable number of disk drives in each row. In some embodiments, one or more variable-width air-flow blocks (or spacers)  1771  and  1772  are provided to fill the space or spaces that are not currently occupied by disk drives. In the embodiment shown, two disk drives  120  and  1120 ′ are initially provided, and variable-width air-flow blocks  1771  and  1772  (e.g., each including a stack of disk-drive-width spacers, equal in number to the missing disk drives) are provided to fill all the other disk-drive spaces. In other embodiments, the disk drives are inserted at the front or back end of the row, and a single spacer (e.g.,  1771 ) is used. As additional drives are inserted into system  1700 , the widths of air-flow blocks  1771  and/or  1772  are decreased. In this way, row  1650  is able to accommodate a variable number of disk drives and maintain appropriate air flow around all of those disk drives that are provided. Reference numbers in  FIG. 17  that are not explicitly described here refer to elements discussed previously and shown in earlier Figures. In some embodiments, the shape of row  1750  is straight and oriented at a right angle to air inlet side  1718 , similar to row  1150  as shown in  FIG. 11 . In some embodiments, the variable-width air blocks  1771  and  1772  are adjustable in different increments, to accommodate the varying spacings between disk drives from the front to the back of the row. In some embodiments, the shape of row  1750  is straight and oriented at an acute or diagonal angle to the air inlet side, similar to row  1250  as shown in  FIG. 12 . In some embodiments, the shape of row  1750  is curved and at an acute angle to air inlet side  1718 , similar to row  1350  as shown in  FIG. 13 . In some embodiments, adjacent pairs of disk drives in row  1750  is staggered, similar to row  1450  as shown in  FIG. 14 , as well as being curved (e.g., as in  FIG. 13 ) and/or at a diagonal angle (e.g., as in  FIG. 12 ) and/or at a right angle (e.g., as in  FIG. 11 ). In some embodiments, two or more such rows (either as shown or mirror image, or alternating as shown and mirror image—e.g., as in  FIG. 16 ) are arranged side-by-side in a single enclosure. 
     In some embodiments, the number of functionally utilized disk drives is fewer than the number that could be placed in an enclosure (e.g., one-hundred-seventy-two of a possible one-hundred-ninety-two, in some embodiments (e.g., four rows of forty-eight drives per row)) and a variable number of spare drives are provided (e.g., up to twenty spare drives, in some embodiments), wherein the number of spare drives provided is variable and set by calculating the number needed to provide a given system lifetime to a given probability (e.g., ninety-eight percent probability of lasting three years without running out of spares, or 99.9 percent probability of lasting five years without running out of spares). Given a predicted failure-rate curve for the entire population of disk drives, the number of disk drives to be used functionally, and perhaps other parameters such as the expected temperature inside the enclosure over time), the number of spare drives needed is calculated. In other embodiments, the total number of drives is fixed (e.g., one-hundred-ninety-two disk drives), and the number of disk drives to be used functionally (and thus the total data capacity) is varied, such that the other drives provide sufficient spares for the expected lifetime of the enclosure. 
     In some embodiments, the enclosure is delivered to the customer with a stated total capacity (based on the number of disk drives to be used functionally, e.g., one-hundred-seventy-two), and with a given number of spare drives (e.g., twenty). Over time, individual ones of the functional disk drives will fail and be replaced using the spare drives. In some embodiments, the data on each drive is mirrored on a corresponding disk drive of an adjacent row, and the data space is striped over a row of drives. In some embodiments, if one drive of such a mirrored pair fails, its data is reconstructed to both drives of a spare pair of drives using data from the mirror drive of the failed drive, and the spare pair will thereafter be used in place of the pair with the one failed drive. For example, the above enclosure could be configured as eighty-six pairs of functional drives and ten pairs of spares (i.e., totaling one-hundred-ninety-two disk drives). During an initial “pair-of-drives-swap” phase, if either drive of a pair fails, a spare pair is loaded with recovered data from the remaining good drive, and that spare drive is swapped for the pair having one failed drive. Later, once all the paired spares have been used to replace pairs of disk drives (each pair having only a single drive that has failed and another drive that is still good), a second “single-drive swap” phase is used, wherein when a single-drive failure is detected, its recovered data is placed on the remaining single good drive of one of the pairs that was swapped out. In some embodiments, during the initial “pair-of-drives-swap” phase, the reduced rotational vibration (RAV) characteristic is maintained by swapping a pair of drives having reduced RAV (e.g., counter-rotating drives or drives at orientations, e.g., at right angles, that reduce RAV effects) for a pair having a failed drive, and during the later “single-drive swap” phase, the slight loss or reduction in RAV resistance is tolerated or compensated for by somewhat reduced performance. 
       FIG. 18  is a perspective view block diagram of a data-storage system  1800  of some embodiments of the invention that provides one or more rows  1750  of disk drives  120  in an upper portion of the enclosure and one or more power supplies in an adjacent lower portion of the enclosure. In some embodiments, one or more rows  1750  of disk drives are connected to the top side of connector plate or circuit board  1500 . In some embodiments, each disk drive is a 0.35-inch (9 mm) thick, 2.5-inch (6.35 cm) form-factor unit that is plugged into a corresponding socket (e.g., either parallel ATA (PATA), serial ATA (SATA) or serial SCSI (SSCSI)) that is soldered to the upper surface of connector board  1500 . In some embodiments, one or more power supplies  1866  are connected to the lower surface of connector board  1500 . Reference numbers in  FIG. 18  that are not explicitly described here refer to elements discussed previously and shown in earlier Figures. 
       FIG. 19  is a cutaway side view of a data-storage system  1900  of some embodiments of the invention that provides a high density enclosure having one or more rows of disk drives. Reference numbers in  FIG. 19  that are not explicitly described here refer to elements discussed previously and shown in earlier Figures. In some embodiments, a first face  1121  of each disk drive (e.g.,  120  and  1120 ′) is facing one direction (left in the figure) along the axis of row  1150  and the opposing second face  1122  is facing the opposite direction (right in the figure) along row  1150 . For example, in some embodiments, for each disk drive, the first face  1121  includes a metal cover  1123  that covers the disks and actuator and opposite side (second face  1122 ) includes a printed circuit card  1124  that holds the electronics for the disk drive  120 . Along one side (e.g., the side facing the viewer in  FIG. 19 ) of disk-drive row  1150  is an air-inlet manifold that conveys inlet air  1113  to the closer edge of the disk-drives  120  in row  1150 . Along one side (e.g., the side facing the viewer in  FIG. 19 ) of disk-drive row  1150  is air-inlet manifold  1112  that conveys inlet air  1113  to one edge of the disk-drives  120  in row  1150 . The bottom edge (as viewed in  FIG. 19 ) of each disk drive  120  has a connector (e.g., two rows of pins) that connects to connector  1923  that is mounted to connector board  1500  (e.g., in some embodiments, connector  1923  is a socket configured to receive the pins of the disk-drive connector). In some embodiments, a resilient (e.g., elastomeric or visco-elastic) boot (or other shape that connects disk drive  120  to connector board  1500  and/or to connector  1923 )  1972  provides a mechanical connection between each disk drive  120  and connector board  1500  that absorbs vibrations (such as from actuator-caused rotational acceleration or vibration) that otherwise would be transmitted from one disk drive  120  to another  1120 ′. In some embodiments, at the opposite side (e.g., the top of each drive in  FIG. 19 ), an adhesively connected resilient (e.g., elastomeric or visco-elastic) disk-drive-cap material  1971  connects the side or edge opposite the connector edge of each disk drive  120  to top cover  1970  (e.g., a plate of sheet steel or aluminum or reinforced composite). Disk-drive-cap material  1971  provides mechanical support for each disk drive  120  by providing a double-sided adhesive structure that, together with connector  1923  and/or boot  1972 , holds the disk drive in place. In some embodiments, disk-drive-cap material  1971  provides a vibration-dampening function (e.g., absorbing vibration energy and converting it to heat). In some embodiments, no screws, shuttles, or other mechanical structures are used to hold drives  120 . This allows more moving air  1111  to contact and cool the disk drives  120 , reduces weight of data-storage system  1900 , and simplifies and reduces the cost of assembly. In some embodiments, one or more power supplies  1866  have pins  1867  that are soldered to through holes in connector board  1500  and power supplies  1866  are thus attached to the bottom side of board  1500  opposite the disk drives. In some embodiments, bottom cover  1979  (e.g., a plate of sheet steel or aluminum or reinforced composite) is placed in contact with a surface of power supply  1866  to provide a heat spreader/heat sink, and air passes around the lateral sides of power supply  1866 . 
       FIG. 20A  is an elevation view of a data-storage system  2000  of some embodiments of the invention that provides a high density enclosure having one or more rows of disk drives arranged in coupled pairs of counter-rotating disk drives. In some embodiments, data-storage system  2000  is similar to system  1900  of  FIG. 19 , except that at least some of the disk drives  120  are placed back-to-back (within a pair) and front-to-front between pairs. Further, in some embodiments, a perforated plate  2073  (e.g., a plate of sheet steel or aluminum or reinforced composite) is provided (in some embodiments, in place of the boots  1972  shown in  FIG. 19 , or, in other embodiments, in addition to boots  1972 ) such that an opening is provided for each of a plurality of disk drives  120 , and a resilient (e.g., elastomeric or visco-elastic) material  2074  bridges at least some of the gaps between the disk drives  120  and plate  2073 . In some embodiments, resilient material  2074  is much larger in height and width than is shown in  FIG. 20A , and provides significant dampening of vibrations of drives  120 . In some embodiments, the height of plate  2073  with respect to the connector edge of the disk drives is variable, in order to be able to select a position that best dampens vibrations. In some embodiments (for example, movable by screw adjustment to different distances from connector board  1500 ), the height of plate  2073  with respect to the connector edge of the disk drives is different for various drives in a single enclosure, in order to be able to select a configuration that best dampens vibrations. In some embodiments, a plurality of fans  1614  and  1615  (optionally in differing vertical positions) are provided to urge air flow through the enclosure, both around and/or in between (e.g., flow  1111 ) disk drives and around and/or between power supplies  1866 . In the embodiment shown, fan  1614  provides both flows  1813  and flows  1111 , while fan  1615  provides mainly flows  1111 . In some embodiments, a plurality of other disk drives  120  are faced in alternating directions to the left and right of the disk drives  120  shown here, in order to help cancel or reduce rotational accelerations transmitted between disk drives  120 . 
     In some embodiments, a large plurality of disk drives (e.g., in some embodiments, the number of drives equals 48, 50, 96, 100, 150, 172, 192, 200, or more disk drives, and four, six or more power supplies) are adhesively held in the enclosure of system  2000 , with a sufficient number of spare drives (e.g., ten, 16, 20, or more spare disk drives) such that the enclosure can be placed in service with the expectation and probability that enough spares have been provided to allow the system to remain in service for the expected lifetime (e.g., three years or five years or other selected periods) without needing a field-service call. 
       FIG. 20B  is an elevation view of a data-storage system  2001  of some embodiments of the invention that provides a high density enclosure having one or more rows of disk drives with an adjustable-height mid-drive vibration damper  2075 . In some embodiments, mid-drive damper  2075  is made of or includes a visco-elastic material, elastomeric material, resilient material, or the like. In some embodiments, a metal grid such as grid  2073  of  FIG. 20A  is embedded in, placed under, or otherwise supports damper  2075 . In some embodiments, at the opposite side from the electrical connector (e.g., the top of each drive in  FIG. 20B ), an adhesively connected resilient (e.g., elastomeric or visco-elastic) disk-drive-cap material  1971  connects the side or edge opposite the connector edge of each disk drive  120  to top cover  1970  (e.g., a plate of sheet steel or aluminum or reinforced composite or the like). Disk-drive-cap  1971  and mid-drive damper  2075  provide mechanical support for each disk drive  120  by providing adhesive structures that, together with connector  1923  (and/or boot  1976  shown in  FIG. 20C ), hold the disk drive in place. In some embodiments, disk-drive-cap  1971  and mid-drive damper  2075  provide a vibration-dampening function (e.g., absorbing vibration energy and converting it to heat). In some embodiments, disk-drive-cap  1971  is omitted, leaving the mid-drive damper  2075  to provide the support and vibration-absorption functions. In some embodiments, no screws, shuttles, or other mechanical structures are used to hold disk drives  120 , but rather disk-drive-cap  1971  and mid-drive damper  2075  together with connector  1923  provide the only support and fastening for disk drives  120 . 
       FIG. 20C  is an elevation view of a data-storage system  2002  of some embodiments of the invention that provides a high density enclosure having one or more rows of disk drives with a cast-in-place vibration-damper boot  2076 . In some embodiments, the disk drives  120  are inserted into their respective socket (or other electrical connector)  1923 , and a liquid or flowable dampening material is poured, injected, or otherwise placed around the base of each disk drive  120 , and solidified (e.g., by thermal, chemical, photonic, or other means) to form vibration-damper boot  2076 . In some embodiments, one or more openings  2080  are provided in connector circuit board  1500  that allow the visco-elastic material to flow between board  1500  and power supply  1866  to provide additional dampening properties. 
       FIG. 20D  is an elevation view of a data-storage system  2003  of some embodiments of the invention that provides a high density enclosure having one or more rows of disk drives with a cast-in-place mid-drive vibration damper  2077 . In some embodiments, a mold  2078  (such as a sheet of stretchy plastic film having a slit or other suitable opening to fit over each disk drive  120 ) is placed over a plurality of the disk drives  120 , and a liquid or flowable vibration dampening material is poured, injected, or otherwise placed onto mold  2078  around a selected mid-point  2081  each disk drive  120 , and solidified (e.g., by thermal, chemical, photonic, or other means) to form mid-drive vibration-damper  2077 . In some embodiments, the mid-point location  2081 , at which mid-drive damper  2077  is placed, is not half-way between connector end  2082  and opposite end  2083  of each drive, but is at some height around each disk drive that is selected to improve vibration dampening. In some embodiments, the height is selected to be at approximately the center of rotational vibration mass of each disk drive  120 . In some embodiments, mold  2078  is a stretchy tube that is placed around the disk drives  120  and which is filled with a material (such as a gas, liquid, or a material that solidifies) in order to stretch the tube into contact with drives  120 . In some such embodiments, the tube is made of an adhesive-coated resilient (e.g., elastomeric or visco-elastic) plastic material. 
     In some embodiments, two or more of the vibration dampening structures such as boot damper  1972 , cap damper  1971 , mid-drive damper  2073  and  2074 , mid-drive damper  2075 , boot damper  2076 , and/or mid-drive damper  2077  are used in a single enclosure to combine to provide improved dampening. 
       FIG. 21  is a front elevation view of a data-storage system  2100  of some embodiments of the invention that provides a high density enclosure having one or more rows of disk drives  120  with one or more vertical beam stiffeners  2110  and optional vibration damper  2122 . System  2100  includes an enclosure  2101  having side walls  2115 , bottom plate  1979  and top cover  961 . In some embodiments, one or more side walls  2115  and/or covers  1979  and  961  are at least partially coated (e.g., on their inside surfaces) with a visco-elastic vibration-dampening sheet  2121 ,  2120  and  2123 , respectively. In some embodiments, visco-elastic vibration-dampening sheet  2121 ,  2120  and  2123  are attached on the inside, and in other embodiments, they are on the outside. In some embodiments, one or more side walls  2115  and/or covers  1979  and  961  are at least partially coated (e.g., on their outside surfaces) with an ESD coating  2116  to dissipate static electric charge. In some embodiments, vertical beam stiffeners  2110  are attached to connector circuit board  1500  and/or drive cap plate  1972  using elastomeric or visco-elastic material  2111 . In some embodiments, visco-elastic vibration-dampening sheet  2120  is also adhesively attached (e.g., across most or all of their bottom surfaces) to power supplies  1866 . In some embodiments, connector circuit board  1500  is held in place using elastomeric or visco-elastic material  2112 . In some embodiments, controller card  960  is attached (e.g., by a plug-and-socket  965 ) to center circuit board  966 . In some embodiments, elastomeric or visco-elastic material  1971  is adhesively attached to the top of each disk drive  120  to hold it in place (rather than using metal or plastic shuttles or other holding devices. In some embodiments, a stiffening ridge  2172  is welded to or attached using elastomeric or visco-elastic adhesive material to cap plate  1972  and/or bottom plate  1979 . In some embodiments (not shown) a similar stiffening ridge is added to top cover  961 . 
     Read-Splitting: Read-splitting is an important and valuable technique for increasing the performance of disk arrays that use pairing. In some embodiments, data is “mirrored” to two or more drives (in a set of M drives, where M is two or greater, each data write from the system causes the same data to be replicated and written to each of the M drives). The data can be striped as well (for example, eight drives can be configured as mirror-four and stripe-two, such that each write operation is replicated four times, and if the block spans more than one drive, each of the four sets of data is striped across two drives; alternatively, the data could be mirrored-two and striped-four, where the data is replicated twice, and long pieces of data are striped across four drives). 
     In some embodiments, when reading, every Mth read operation goes to the first drive of a set, every M+1 st  read goes to the second drive, etc. This reduces the utilization of each drive, since only 1/M of the reads are directed to each drive. In other embodiments, each read operation is sent to all drives, and the first drive to return data has its data used, and the other drive&#39;s data is ignored or discarded. This increases the speed of retrieval, since the fastest drive provides the data. 
     Embodiment C1 
     Read-Splitting Using Vibration-Interaction Mapping (e.g., Wherein Physical Location of Drives Determines which Drive is Used for a Particular Read Operation) 
     When data is read from a plurality of mirrored or striped/mirrored drives using read-splitting logic in the RAID controller or software, it can be highly unlikely that an I/O request to logical disk will cause simultaneous actuator movements among mirrored physical disk drives, and it is problematic to try to predict the direction and duration of these accelerations with respect to nearby disk drives. Rather, read-splitting and bus/loop arbitration logic among the disk drives makes it likely that these accelerations will be random with respect to other drives, and therefore also likely that RAV energy created by one disk of a mirrored set that is seeking will be transmitted to a nearby disk (the “subject” disk) that is in the process of transferring data to/from the media, making the subject disk particularly vulnerable to RAV. 
     In some embodiments, a coordinated logical to physical mapping of mirrored disk drives via RAID ensures that mirrored HDA&#39;s are oriented orthogonally (Embodiments B1, B2, and the like) to one another, while striped HDAs are oriented with alternating rotational directions (Embodiments A1, A2, and the like). 
     In some embodiments, a first data structure is kept (e.g., in the enclosure&#39;s controller-card memory) that maps the physical location (see Table 1B below) and/or drive-to-drive vulnerability (see Table 1A below) of each drive of each mirrored set, and a second data structure is kept that indicates the state (e.g., idle, seeking, reading, or writing, etc., and/or the actuator location or address of last data block accessed) of each drive. In some such embodiments, read splitting is used, wherein the determination of which drive of a mirrored set is selected to use for a given read-split read operation is based, at least in part, on the state of nearby drives that could be affected by sending a seek operation to a given drive. For example, if a read command is received by the enclosure&#39;s controller card that could be satisfied by sending the command to any one of a plurality of drives in a mirrored set, for each drive that can provide the requested data the controller examines the state (as specified by the second data structure) of the nearby or most vulnerable drives (as specified by the first data structure), and the controller then selects the drive that is least likely to cause an error in its neighboring drives. 
     In some embodiments, the content of the first data structure, for each drive in the enclosure, specifies which other drives are most vulnerable to an RAV error due to a seek operation, and optionally specifies the magnitude of vulnerability (the probability of an induced RAV error). In some embodiments, the content of the first data structure is determined, at least in part, by the physical location and/or orientation of each drive. In some embodiments, the content of the first data structure is determined, at least in part, by an empirical measurement, for each drive, of the drive-to-drive vulnerability as measured by establishing a read-tracking mode in a subject drive and then performing a seek operation of a given magnitude in the drive being tested. For example, when determining the neighboring-drive-vulnerability mapping of the first drive (the seek drive), one at a time each one of the neighboring drives (the victim drive) is forced into a state of read tracking, the first drive is then made to perform a seek operation, and it is determined whether the victim drive suffered a tracking error as a result of the seek. In some embodiments, this is repeated a number of time to ascertain the probability of a tracking error being caused. In some embodiments, a plurality of different seek amounts or magnitudes (e.g., small, medium, or large) is tried for each seek drive during the data structure generation, and the resulting tracking-error probabilities are determined for each of the other drives in the enclosure. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1A 
               
             
            
               
                   
                   
               
               
                   
                 Large seek or 
                   
                   
               
               
                   
                 large rotation acceleration vibration (RAV) 
                 medium seek or RAV 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Data 
                   
                 error 
                   
                 error 
                   
                 error 
                   
                   
                 error 
                   
                 error 
                   
                 small seek or RAV . . . 
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Structure 1 
                 Victim 
                 prob- 
                 Victim 
                 prob- 
                 Victim 
                 prob- 
                   
                 Victim 
                 prob- 
                 Victim 
                 prob- 
                   
                 Victim 
                 error 
                   
                 . . . 
               
               
                 Seek Drive 
                 drive 
                 ability 
                 drive 
                 ability 
                 drive 
                 ability 
                 . . . 
                 drive 
                 ability 
                 drive 
                 ability 
                 . . . 
                 drive 
                 probability 
                 . . . 
                 . . . 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 1 
                 2 
                 .6 
                 5 
                 .5 
                 17 
                 .15 
                 . . . 
                 2 
                 .4 
                 5 
                 .1 
                 . . . 
                 2 
                 .05 
                 . . . 
                 . . . 
               
               
                 2 
                 1 
                 .55 
                 4 
                 .4 
                 17 
                 .3 
                 . . . 
                 1 
                 .3 
                 4 
                 .2 
                 . . . 
                 1 
                 .03 
                 . . . 
                 . . . 
               
               
                 3 
                 2 
                 .24 
                 44 
                 .24 
                 1 
                 .08 
                 . . . 
                 2 
                 .14 
                 4 
                 .14 
                 . . . 
                 2 
                 .024 
                 . . . 
                 . . . 
               
               
                 . . . 
                   
                   
                   
                   
                   
                   
                 . . . 
                   
                   
                   
                   
                 . . . 
                   
                   
                 . . . 
                 . . . 
               
               
                 N 
                 147 
                 .1 
                 145 
                 .09 
                 12 
                 .07 
                 . . . 
                 147 
                 .1 
                 145 
                 .07 
                 . . . 
                 147 
                 .02 
                 . . . 
                 . . . 
               
               
                   
               
            
           
         
       
     
     In use, suppose a read-split read is received and can be serviced by either drive  1  or drive  3  (since the requested data is replicated/mirrored on these two drives). If all the drives in row  1  and row  3  of data structure  1  are idle, then the enclosure controller can send this read operation to whichever drive ( 1  or  3 ) would have the shortest seek or the least rotation acceleration, or a random choice or ping-pong (i.e., alternating successive reads between these two data sources) choice between drive  1  and  3  could be made. Suppose, however, that drive  5  is in a read-tracking state: the entries for drive  1  show that there is a non-negligible error probability (0.50) that a tracking error will occur if the specified seek (suppose a large seek for this example), while the entries for drive  3  do not indicate that an error is probable for drive  5  if a seek is performed on drive  3 . Accordingly, the read-split read command will be directed to drive  3 , since there is little or no likelihood that a tracking error would result. Note also that, in some embodiments, data structure  2  provides actuator-location information for each candidate drive, which when compared to the address of the incoming read-split read command, provides the indication of the size of the seek operation (i.e., the magnitude of the acceleration vibration that will be generated). In some embodiments, data structure  2  provides a parameter for each drive of the enclosure&#39;s relative flexibility or stiffness at that drive&#39;s location (and/or the node-antinode parameter that indicates how close to or far from a standing-wave-resonance node that drive is positioned). In some embodiments, this stiffness and/or node parameter is an input into the formula used to determine the size of the seek or rotational acceleration vibration that is used as an input to Table 1A (i.e., if a drive is positioned at a stiff location or near a resonance node, a seek that would cause a “Large” RAV on another drive might cause only a medium or small RAV for this drive). 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                 TABLE 1B 
               
               
                   
               
               
                   
                   
                 drive-drive 
                   
                 drive-drive 
                   
                 drive-drive 
                   
               
               
                 Data Structure 1 
                   
                 spacing, 
                   
                 spacing, 
                   
                 spacing, 
               
               
                 Seek Drive 
                 Victim drive 
                 orientation 
                 Victim drive 
                 orientation 
                 Victim drive 
                 orientation 
                 . . . 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 1 
                 2 
                 6.0 cm, parallel 
                 5 
                 5.0 cm, 
                 17 
                 1.5 cm, 
                 . . . 
               
               
                   
                   
                   
                   
                 60 degrees 
                   
                 in-line 
               
               
                 2 
                 1 
                 6.0 cm. parallel 
                 4 
                 4.0 cm, 
                 17 
                 3.0 cm, 
                 . . . 
               
               
                   
                   
                   
                   
                 parallel 
                   
                 parallel 
               
               
                 3 
                 2 
                 2.4 cm, 
                 44 
                 2.4 cm, 
                 1 
                 0.8 cm, 
                 . . . 
               
               
                   
                   
                 orthogonal 
                   
                 20 degrees 
                   
                 orthogonal 
               
               
                 . . . 
                   
                   
                   
                   
                   
                   
                 . . . 
               
               
                 N 
                 147 
                 1 cm, 
                 145 
                 19 cm, 
                 12 
                 17 cm, 
                 . . . 
               
               
                   
                   
                 facing 
                   
                 25 degrees 
                   
                 parallel 
               
               
                   
               
            
           
         
       
     
     Rather than or in addition to Table 1A that tracks the drive-drive vulnerability to errors, in some embodiments, a data structure such as Table 1B is kept that stores the distance and/or relative orientation and/or node-antinode positioning and/or relative stiffness between a plurality of pairs of drives. Table 1B is used in a manner similar to the use of Table 1A, in that an incoming read-split read operation is received by the enclosure controller, which then makes a choice between the possible source drives for the requested data based on the distance, orientation, node-antinode positioning, and/or relative stiffness between the selected drive and other drives that are in a state that makes them vulnerable to RAV-induced tracking errors. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                 Actuator 
                 Enclosure relative flex- 
               
               
                 Data 
                   
                 location or 
                 ibility or stiffness 
               
               
                 Structure 2 
                   
                 sector last 
                 at drive location, 
               
               
                 Drive 
                 Drive state 
                 accessed 
                 or node-antinode 
               
               
                   
               
             
            
               
                 1 
                 Idle 
                 track 3047 
                 5 
               
               
                 2 
                 Idle 
                 track 1540 
                 8 
               
               
                 3 
                 Seek 
                 track 10 
                 1 
               
               
                 4 
                 write tracking 
                 track 30205 
                 7 
               
               
                 5 
                 read tracking 
                 track 1540 
                 6 
               
               
                 . . . 
               
               
                 N 
                 Idle 
                 track 4222 
                 2 
               
               
                   
               
            
           
         
       
     
     Cabinet design: One problem addressed by this present invention is created when rotational vibration (movement that revolves around the axis of the actuator motor), usually from another drive, rotates the drive relative to the actuator, and thus pulls the head off the track it is reading from or writing to. With drives that are mounted vertically, one problem is that RAV that raises or lowers one corner  119  of the drive  120 , and/or lowers or raises the opposite corner  121  in the other direction. 
     One aspect of some embodiments of the present invention includes positioning and orienting each drive to achieve a desired flow pattern and volume of cooling air through the enclosure. Another aspect of some embodiments of the invention includes positioning drives in the enclosure with a spacing, orientation, and/or location so as to reduce or minimize drive-to-drive RAV induced tracking (or other) errors. Another aspect of some embodiments of the invention includes timing and/or synchronizing access commands that are sent to the drives in the enclosure so as to reduce or minimize drive-to-drive RAV induced tracking (or other) errors. 
     In some embodiments, the disk drives are electrically connected to a connector on the disk-drive-connector circuit board  1500 , but are held in place in the enclosure primarily using a visco-elastic material that contacts each disk drive at one or only a few locations to ensure that the disk drive remains connected to the connector, are allowed to move slightly within the constraints of the visco-elastic holder, have their vibrations dampened by the visco-elastic holder, and still have a substantial surface area exposed to the air flow through the cabinet to cool the drives. By eliminating the metal or plastic shuttle and/or screws that are typically used to hold a disk drive in place, a substantial weight reduction is achieved. 
     In some embodiments, because of the large number of operational disk drives, and the large number of spare disk drives that can be swapped in if there is a failure detected, the drives can be sealed in place, for example, by adhering every disk drive to the visco-elastic holder, and adhering the visco-elastic holder to the enclosure. The large number of operational and spare drives also allows meaningful statistical analysis of the failure rate and a determination of where the unit is in the life cycle of the enclosure. A typical expected life of the enclosure can be tailored by adjusting the number of spare drives, for example, yielding a unit having a three-year expected lifetime with more usable operational data storage space (e.g., using fewer spare drives, e.g., perhaps ten initial spare drives and one-hundred-ninety operational drives), or yielding a unit having a five-year expected lifetime with less usable operational data storage space (e.g., using more spare drives, e.g., perhaps twenty-five initial spare drives and one-hundred-seventy-five operational drives). 
     Controller design: Another aspect of some embodiments of the invention includes mirroring or replicating data on a plurality of drives (which improves reliability and/or performance) so that each read command can be directed to one or more drives in order to shorten access time (if the same command is sent to two or more drives, the one that returns the data fastest is used, which improves performance), reduce the average drive utilization (the command is sent to fewer than all the drives that have the data, so that the other drives remain available to perform other operations, which can also improve performance). In some embodiments, one of a plurality of drives containing the data is selected based at least in part on whether nearby or vulnerable drives would suffer errors as a result (e.g., based on such parameters as what state each of the other drives is in (e.g., read-tracking, seeking, or idle), the relative probability that a seek in a selected drive will cause an error in another drive, the distance between drives, the relative orientation, stiffness, node-antinode positions, etc.). 
     Another aspect of some embodiments of the invention includes sending substantially simultaneous and substantially the same size seek commands to counter-rotating drives that are positioned relative to one another so that the rotational accelerations cancel, at least to some extent. The term “counter-rotating drives” means a set of drives configured such that for every drive that receives a given seek command that causes a given rotational acceleration around an axis, there is another drive positioned such that the same seek command will cause substantially the same rotational around substantially the same axis but in the opposite rotational direction (thus canceling some or all of the RAV seen by other drives). Such a set of drives can have any even number of drives in the set (2, 4, 6, etc.). Data can be mirrored and/or striped across the set of drives in order to have many or all of the commands sent to the set of counter-rotating drives provide the RAV-canceling function. 
     Striping using two or more disk drives to send opposing rotational accelerations; and/or counter-rotating pairs; each drive in a pair physically facing the other: In some embodiments, a plurality of the drives are placed in opposite-facing pairs (either front-to-front, or back-to-back). The system stripes all writes and reads so 1/N (half the data if mirrored pairs of drives are used; N=2) of the data goes to each clockwise drive and 1/N (or half) of the data is sent to each counterclockwise drive (in a pair, both drives move their respective actuators the same direction and amount, either both “clockwise” or both “counterclockwise” for a given access relative to their own top cover, but since they are face-to-face, simultaneous clockwise accelerations are in opposite directions relative to an outside frame of reference). The system-level sectors are N times (e.g., twice if N=2) as big as drive sectors. In some embodiments, all seek accesses that move the actuator are sent simultaneously to the CW and CCW drive of a pair so the rotational moments cancel within the pair. In some embodiments, the timing of the seek operations is synchronized to better cancel the rotational acceleration. The pair is mounted rigidly or semi-rigidly to one another, but held with elastomer or visco-elastic to the case so the rotational changes cancel within the pair and do not transfer to the case. In some embodiments, the “simultaneous” pairs of seeks do not occur at the same time, but both seek portions take place while the other drive is preparing to do its seek or has just finished its seek acceleration, but has not started to do the read or write portion. Thus, both seek portions take place during a first portion of the operation when the other drive is not trying to stay on track but is still settling to its desired track, and the data-access portions both take place in a second portion of the operation when the other drive is not seeking. During the first portion, both drives are in a less-vulnerable state and can tolerate more RAV. During the second phase, both drives are in the more-vulnerable read or write mode where they must stay on track to avoid losing performance or data, and neither is generating RAV to disturb the other. 
       FIG. 4A , for example, shows a pair of disk drives  120  and  120 ′ plugged into connectors on bottom membrane  150 . 
     In Some Embodiments, Avoid In-Line Or L-Type Orthogonal Positioning; Use T-Type Orthogonal Positioning: Drives are most sensitive to rotational-acceleration vibration (RAV) moves. To correct for this, in some embodiments, the corner of one drive is placed at the rotational “center” of next drive. Some embodiments use a T-orientation. In some embodiments, drives are placed in pairs as described above, and each pair is placed at an angle (e.g., a T-type right angle) to an adjacent pair. 
     Orthogonal or Staggered Positioning—Herringbone But With Rotational Moments of Inertia of One Drive (i.e., the Corner) Positioned at the Actuator Center or Rotational Center-of-Mass of Adjacent Drive: What starts as rotational torque around the Z R -direction can be made to be X- or Y-movement to drives that are at right angles, and even to drives that are at other intersecting angles. For example, positioning a first corner of a first drive next to the center of rotational mass of an adjacent second drive means that rotational torque that moves the first corner downward is downward movement at the center of rotational mass of the second drive, and thus will move the entire second drive down rather than rotating it. Further, the angled orientation (intersecting planes of the disk drives) provides additional stiffening of the enclosure, particularly in embodiments where the bottom edge of each drive is held to the connector circuit board  1500  and the top edge is adhesively held, for example, to a visco-elastic sheet that is adhesively held to a top plate (e.g., a sheet-metal enclosure cover). This arrangement also allows a large amount of the total exterior surface of each drive to be exposed to the flow of cooling air, and for the disk drives themselves to serve as air vanes and/or heat-sink fins to direct the flow of the cooling air flow. 
     Add walls and/or I-beams as stiffeners parallel to major face of drives-perpendicular to dotted lines that connect adjacent corners of drives: Some embodiments add walls  2110  and/or ridges  2172  at right-angles to the bottom and/or top enclosure surface (which act as vibrational membranes). These stiffeners reduce vibration transferred between drives. Stiffener walls can be added across what would otherwise be antinodes, discussed below. In some embodiments, visco-elastic dampening materials  1971 ,  2120 ,  2121 , and/or  2123  are applied to walls  2121 , or enclosure surfaces  961 ,  1979 , and/or  1972  to dampen vibrations and reduce noise. 
     Use the array-controller card as I-beam stiffener down center of case, between rows of drives: In some embodiments, center controller card  966  (e.g., the card that receives commands from other units and passes the appropriate commands to the drives, buffers data, and/or does RAID generation and correction of data) can act as an alternative or additional stiffener to the walls discussed above. 
     Include a visco-elastic dampener to attach face of controller PC board to face of steel or fiberglass I-beam: A visco-elastic adhesive or other such material attached across a wall face acts to dampen vibrations in that wall. In some embodiments, visco-elastic material with one or more adhesive faces is adhered to such walls and other enclosure covers, and/or is used to connect walls to bottoms, covers, and intermediate structures to stop transmission of vibrations from one structure to another. In some embodiments, visco-elastic material is adhered to circuit boards as well. 
     Include a visco-elastic dampener to attach one or more I-beams to top and/or bottom covers: A visco-elastic adhesive attached between walls at right angles to one another (e.g., to connect them to each other) acts to dampen vibrations that would otherwise transfer between those walls. 
     Place drives at node (lesser-vibrating) positions of the standing-wave pattern of the bottom membrane of the disk—drive array enclosure: Conventional multi-drive disk storage subsystems place all the disk drives adjacent an outer surface, typically each one with one of its two smallest faces pointing outward along the front panel of the enclosure, with the opposite small face, having the connectors, plugged into an outward-facing connector socket. This is needed in order to have access to drives in case they need to be serviced or replaced in the field (e.g., by hot-unplugging the failed drive and hot-plugging the new replacement drive in its place). 
     In contrast, some embodiments of the present invention include a much-larger number of physically small drives mounted in their enclosure in a manner intended not to be replaced in the field, and with a sufficient number of spare drives that can be logically swapped in place to the number of drives that could be expected to fail during the service life of the system. The operating drives are known as “fail-in-place” drives, since if and when they fail, the failed drive is left physically in place in the enclosure, and one of the spare drives is logically connected in its place and loaded with reconstructed data of the failed drive. 
     Two-dimensional surfaces (membranes) have vibrational-resonance patterns that are affected by the constrained edges (such as the outer edges of the bottom surface of the multi-drive enclosure disk storage system) 
     Some embodiments place drives in a pattern in the enclosure that matches more closely the non-vibrational node locations of the “membrane” surfaces (e.g., the bottom cover and/or wiring grid) to which they are attached. On a membrane, standing waves form a two-dimensional pattern, in which the constrained edges and other locations within the membrane have little or no standing-wave vibration, and other antinode locations have much vibration. The node/antinode locations are affected by the size, shape, and thickness of the membrane, as well as the other masses (e.g., disk drives and controller cards) and stiffeners (e.g., right-angle walls and/or I-beams). In some embodiments, these node and antinode locations are determined empirically by placing the drives on the surface, measuring the vibrational susceptibility and/or the node/antinode pattern (i.e., whether drives in a particular location suffer seek errors, or the magnitude of vibration at each drive as determined by, e.g., vibrational holography, in which a photosensitive film is exposed to the interference pattern between a reference beam, and another beam that is split from the reference beam and illuminates the membrane surface while it is being acoustically stimulated to form standing waves, as is well known in the art), then iteratively moving one drive slightly from its initial position and re-measuring until that drive reaches a point of minimum vibration; then iteratively repeating the process for neighboring drives until each drive is at a point on the membrane that is less or minimally RAV vulnerable (i.e., susceptible to read or write errors from received rotational acceleration vibration of other drives), and/or minimally RAV dangerous (i.e., capable of causing rotational acceleration vibration that is transmitted to other drives). 
       FIG. 4A  is a perspective drawing that illustrates a hard-disk-drive (HDD) or disk drive  120  mounted in a vertical orientation into connector  126  integrated on a substrate printed circuit board (PCB)  150 . The HDD  120  has a side A  190 , a side B  492 , an edge C  194 , an edge D  196 , and a connector  116  on the bottom edge. The HDD  120  has drive electronic circuit board  150  attached to side B  492 . Internal to the HDD  120  is a set of one or more disks  115 , and an actuator assembly  112 . The actuator assembly  112  contains an R/W head  114 . The actuator assembly  112  pivots around an axis of rotation  111  to perform seek operations. 
     When the actuator assembly  112  accelerates in one direction  191  or another to perform a seek operation, there is a corresponding counter rotation force or torque  192  in the HDD  120 , as a whole, producing a rotational vibration. Since the mass of the HDD  120  is many times greater than mass of the actuator assembly  112 , the magnitude of the rotation of HDD  120  produced is much smaller than the magnitude of the actuator assembly rotation. This acceleration-induced torque  192  rotating the HDD  120  produces rotational-acceleration vibration which is transferred to surrounding supporting structures such as the connector  126  and substrate  120 . The characteristic “click, click, click” that can sometimes be heard during actuator seek operations is due partly to the rotational-acceleration vibration of the HDD  120 . Rotational-acceleration vibration generated by drive  120  can cause vibration in neighboring drive  120 ′ through supporting structures. Rotational-acceleration vibration is generally more problematic for closer neighboring drives than those further away. The rotational-acceleration vibration interaction between hard-disk drives (HDDs) can cause actuator assembly seek or tracking problems in close-neighboring drives. The present invention orients each of the drives in an enclosure to reduce or minimize drive-to-drive coupling of rotational vibration. 
     In some embodiments, the invention provides an apparatus that includes a substrate, and a plurality of disk drives each coupled electrically and mechanically to the substrate, the plurality of disk drives including at least a first and a second disk drive, wherein the first disk drive is positioned relative to the second disk drive so that a rotational force produced by the first disk drive is at least partially counteracted by a rotational force produced by the second disk drive. 
     In other embodiments, the apparatus can further comprise an enclosure, wherein the substrate and the plurality of disk drives are attached to the enclosure, at least one memory, and an information processing unit operatively coupled to the disk drives and to the memory, wherein the information processing unit sends read commands to the disk drives and receives data from the disk drives and from the memory. 
     The apparatus can optionally include an information processing unit that includes a multi-processor supercomputer. In some embodiments, the apparatus includes a plurality of substantially similar enclosures, wherein each enclosure holds a substrate and plurality of disk drives including at least a first disk drive and a second disk drive positioned such that a rotational force produced by the first disk drive is conveyed primarily as a translational force to the second disk drive, and wherein the plurality of enclosures are operatively coupled to the supercomputer. 
     In some embodiments, the apparatus further comprises a memory and a video-streaming apparatus operatively coupled to receive data from the memory, wherein the video-streaming apparatus is adapted to transmit digital video to a plurality of destinations and users. In some other embodiments, the plurality of disk drives includes more than two first disk drives in a first rotating orientation and fewer than about one-hundred-and-one first disk drives, and a substantially equal number of second disk drives in a second counter rotating orientation, wherein a plurality of the first and a plurality of the second disk drives are interleaved in coupled pairs. In some embodiments, the plurality of disk drives includes more than about one-hundred first disk drives and fewer than about two-hundred-and-one first disk drives, and a substantially equal number of second disk drives, wherein a plurality of the first and a plurality of the second disk drives are interleaved in coupled pairs, each pair including one disk drive in a rotating orientation, and another disk drive in a counter rotating orientation. 
     In some embodiments of the invention, at least some of the plurality of disk drives are each in contact with a boot unit. In some embodiments, the boot unit includes one or more resilient materials. In other embodiments, the boot unit has graded shock absorbance characteristics. In still other embodiments, the boot unit includes a vibration damping polymer. A boot unit can include a visco-elastic material. In some embodiments of the invention, a first edge of each one of the plurality of disk drives are adhesively connected to its boot unit. In other embodiments, a first edge of each one of the plurality of disk drives is bonded to its boot unit. 
     In some embodiments, an apparatus of the invention can further include a detent device that is adapted to be placed in disengageable contact with each one of the plurality of disk drives at an edge distal from the drive&#39;s first edge. In some embodiments, the detent device is wedge shaped at a first end and adapted to be inserted against each of a plurality of drives for transport and disengaged for disk operation. In other embodiments, the detent device includes a cam mechanism adapted to be engaged for transport and disengaged for disk operation. 
     In some embodiments of the invention, the first disk drive has a disk rotational torque vector due to its rotating disk(s) that is substantially antiparallel to a disk rotational torque vector of the second disk drive that is due to its rotating disk(s). In some embodiments, the disk rotational torque vector of the first disk drive is substantially collinear with the disk rotational torque vector of the second disk drive. In other embodiments, the disk rotational torque vector of the first disk drive is radially offset from the disk rotational torque vector of the second disk drive. In still other embodiments, the actuator rotational torque vector due to actuator arm rotation in the first disk drive is substantially collinear with the actuator rotational torque vector of the second disk drive. 
     In some embodiments, a first major face of each of the first and second disk drive each have a first heat-conduction characteristic and the second opposing major face of the first and second disk drive have a second heat-conduction characteristic that is different from the first heat-conduction characteristic. In some embodiments, the first major faces of the first and second disk drives each are substantially metallic. In other embodiments, the first major faces of the first and second disk drives are each portions of a respective metal cover that covers the respective disk drive&#39;s disk(s) and actuator arm. In still other embodiments, the second major faces of the first and second disk drives each are substantially non-metallic. In some embodiments, the second major faces of the first and second disk drives each include a printed circuit board. In some embodiments, the second major faces of the first and second disk drives each are substantially plastic, such as a fiberglass-reinforced epoxy circuit board. 
     In other embodiments, the first disk drive and the second disk drive are coupled to the substrate with the first major face of the first disk drive facing with a partial offset the first major face of the second disk drive. In still other embodiments, the first disk drive and the second disk drive are coupled to the substrate with the first major face of the first disk drive facing with no offset the first major face of the second disk drive. In some embodiments, the first and second disk drive form a first coupled pair, further including a second coupled pair having a third and fourth disk drive with a first major face of the third disk drive facing with no offset a first major face of the fourth disk drive, and a second major face of the second disk drive facing with partial offset a second major face of the third disk drive. 
     In some embodiments, the apparatus can further include a controller that receives a disk access request specifying a data length of 2L and based on the request sends substantially simultaneous disk access requests to the first and second disk drive each specifying a data length of L. In some embodiments, the substantially simultaneous disk access request sent to the first and second disk drives cause seek operations having rotational forces that at least partially cancel each other. 
     In some embodiments of the invention, the plurality of disk drives are formed into coupled pairs having substantially opposite rotational torque within each pair. In other embodiments, a first edge of each coupled pair is coupled to the substrate and an opposing second edge is coupled to an elastomeric material. 
     In some embodiments, an apparatus can further comprise a stabilizer member having an elastomeric material in contact with at least some of the plurality of the disk drives between the first edge and the second edge of the respective disk drives. In some embodiments, the stabilizer member is a plate member having an elastomeric material in contact with at least some of the plurality of the disk drives between the first edge and the second edge of the respective disk drives. In some embodiments, the plate member is substantially parallel to the first and second edge and includes a plate having perforations that encircle each disk drive. In other embodiments, the plate member further includes an elastomeric material bridging a gap between an edge of a perforation in the plate member and the disk drive encircled by the perforation. 
     In some embodiments, the plurality of first disk drives and second disk drives are oriented as alternately facing coupled pairs. In other embodiments, for each one of a plurality of disk drives, the first major face of the respective drive is spaced closer to its nearest neighbor&#39;s first major face as compared to the spacing of the respective drive&#39;s second major face to its nearest neighbor&#39;s second major face, the second major faces having lower heat conductivity than the first major faces. In some embodiments, for each one of a plurality of disk drives, the first major face of the respective drive is spaced further from its nearest neighbor&#39;s first major face as compared to the spacing of the respective drive&#39;s second major face to its nearest neighbor&#39;s second major face, the second major faces having lower heat conductivity than the first major faces. 
     In some embodiments, the plurality of first and second disk drives are each coupled electrically and mechanically to the substrate in a row that conforms to a line, wherein the first disk drives and the second disk drives are facing in alternate directions positioned within the row. In some embodiments, the row includes two or more disk drives and fewer than two-hundred-and-one disk drives. In other embodiments, each of the first disk drives have a first major face and a second opposing major face and wherein each of the second disk drives have a first major face and a second opposing major face, and wherein the first major face of each first disk drive faces the first major face of an adjoining second disk drive, and the second major face of each first disk drive faces the second major face of an adjoining second disk drive. In some embodiments, the row conforms to a substantially linear line. In some embodiments, the row conforms to a substantially stepped curved line. In other embodiments, the stepped curved line curves in a substantially exponential manner. In still other embodiments, the row conforms to a substantially smooth curved line. In some embodiments, the substantially smooth curved line curves in a substantially exponential manner. In some embodiments, the apparatus includes one or more additional rows of disk drives. In some embodiments, the rows are positioned on the substrate with substantially mirror image orientation relative to a neighboring row. 
     In some embodiments, the apparatus further includes elastomeric material that is attached to the disk drives at a position on each of the disk drives that is opposite the position on the disk drives proximal to the substrate. 
     In some embodiments, the apparatus further includes an enclosure. In some embodiments, the substrate is oriented parallel to a first major surface of the enclosure. In some embodiments, the enclosure of the apparatus includes at least one air inlet and at least one air outlet. In some embodiments, the apparatus further includes at least one manifold that directs airflow over the disk drives. In some embodiments, the apparatus further includes an air-movement-causing device. In some embodiments, the air-movement device includes one or more fans. In other embodiments, the air-movement device includes one or more pairs of fans that rotate in opposite directions. In some embodiments, the enclosure of the apparatus includes a cover. In other embodiments, the cover includes a resilient material. In some embodiments, a resilient material is attached to a second edge of each one of a plurality of the disk drives. In some embodiments, the cover of the apparatus includes at least one stiffening rib. In some embodiments, a resilient material is attached to the cover. In some embodiments, the apparatus further includes a shipping-overshock display. In other embodiments, the apparatus further includes a mother board, a personality board, or any combination thereof. 
     The invention provides a method that includes mounting a plurality of drives in an enclosure, the enclosure including a connector substrate, the plurality of drives including at least a first disk drive and a second disk drive that are each electrically and mechanically coupled to the enclosure, and mechanically coupling the first drive and the second drive such that rotational force produced by the first disk drive is at least partially counteracted by rotational force produced by the second disk drive. In some embodiments, the rotational force produced by the second disk drive is opposite the rotational force produced by the first disk drive. 
     The method can include operatively coupling an information processing unit to the enclosure, and adding a memory to the enclosure, wherein the information processing unit is operatively coupled to the disk drives and to the memory, wherein the information processing unit sends read commands to the disk drives and the receives data from the disk drives and memory. In some embodiments, a multi-processor supercomputer is used as the information processing unit. In some embodiments, a plurality of substantially similar enclosures are operatively coupled to the supercomputer, wherein each enclosure holds a substrate and plurality of disk drives including at least a first disk drive and a second disk drive positioned such that a rotational force produced by the first disk drive is conveyed primarily as a translational force to the second disk drive, and wherein the plurality of enclosures are operatively coupled. 
     In some embodiments, the method includes storing data from the disk drives into a memory, and streaming video information from the enclosure, wherein the streaming video information includes receiving information from the memory and transmitting digital video to a plurality of destinations and users. 
     In some embodiments, the method includes causing a seek operation that results in a rotational force produced by the first disk drive. In some embodiments, the method includes positioning the plurality of disk drives such that a number of the first disk drives, the number being greater than two and fewer than about one-hundred-and-one, are in a first rotating orientation, and a substantially equal number of second disk drives are in a second counter-rotating orientation, wherein a plurality of the first disk drives and a plurality of the second disk drives are interleaved in mechanically coupled pairs. In some embodiments, the method includes positioning the plurality of disk drives such that a number of the first disk drives, which is greater than about one-hundred and fewer than about two-hundred-and-one, are in a first rotating orientation, and a substantially equal number of second disk drives are in a second counter-rotating orientation, wherein a plurality of the first disk drives and a plurality of the second disk drives are interleaved in mechanically coupled pairs, each pair including one disk drive in a rotating orientation, and another disk drive in a counter-rotating orientation. 
     In some embodiments, the method includes damping relative motion between at least some of the plurality of disk drives and the substrate. In some embodiments, the damping includes absorbing vibration energy in one or more resilient materials. In some embodiments, the damping includes absorbing vibration energy in one or more resilient materials that include graded shock absorbance characteristics. In some embodiments, the damping includes absorbing vibration energy in one or more resilient materials that include a vibration damping polymer. In some embodiments, the damping includes absorbing vibration energy in one or more resilient materials that include a visco-elastic material. 
     In some embodiments, the method includes positioning at least some of the plurality of disk drives in contact with one or more boot units. In some embodiments, the method includes providing one or more resilient materials for each one of the plurality of boot units. In some embodiments, the method includes providing one or more resilient materials for each of a plurality of boot units that include graded shock absorbance characteristics. In some embodiments, the method includes providing one or more resilient materials for each of a plurality of boot units that include a vibration damping polymer. In some embodiments, the method further includes providing one or more resilient materials for each of a plurality of boot units that include a visco-elastic material. In some embodiments, the method includes adhesively connecting a first edge of each one of the plurality of disk drives to its boot unit. In some embodiments, the method includes bonding a first edge of each one of the plurality of disk drives to its boot unit. 
     In some embodiments, the method includes placing a detent device in disengageable contact with each one of the plurality of disk drives at an edge distal from a first edge of each one of the disk drives. In some embodiments, the method further includes sliding the detent device, which is wedge shaped at a first end and adapted to be inserted, until it rests against each of a plurality of drives for transport and is disengaged for disk operation. In some embodiments, the method includes camming (rotating a linear element having one or more cams for each disk drive) the detent device that is adapted to be engaged for transport and disengaged for disk operation. 
     In some embodiments, the method includes positioning the first disk drive so that its disk rotational torque vector due to its rotating disk(s) is substantially antiparallel to a disk rotational torque vector of the second disk drive that is due to its rotating disk(s). In some embodiments, the method includes positioning the first and second disk drive such that the disk rotational torque vector of the first disk drive is substantially collinear with the disk rotational torque vector of the second disk drive. In some embodiments, the method includes positioning the first and second disk drive such that the disk rotational torque vector of the first disk drive is radially offset from the disk rotational torque vector of the second disk drive. In some embodiments, the method includes positioning the first and second disk drive such that the actuator rotational torque vector due to actuator arm rotation in the first disk drive is substantially collinear with the actuator rotational torque vector of the second disk drive. In some embodiments, the method includes positioning the first and second disk drive such that the first major face of both the first and second disk drive each have a first heat-conduction characteristic and the second opposing major face of the first and second disk drive have a second heat-conduction characteristic that is different from the first heat-conduction characteristic. In some embodiments, the first major faces of the first and second disk drives each are substantially metallic. In some embodiments, the method includes positioning the first major faces of the first and second disk drives such that they face each other, wherein the first major faces of the first and second disk drives are each portions of a respective metal cover that covers at least a portion of the respective disk drive&#39;s disk(s) and actuator arm. In some embodiments, the method includes positioning the second major faces of the first and second disk drives such that they face each other, wherein the second major faces of the first and second disk drives are each substantially non-metallic. In some embodiments, the method includes positioning the second major faces of the first and second disk drives such that they face each other, wherein the second major faces of the first and second disk drives each include a printed circuit board. In some embodiments, the method includes positioning the second major faces of the first and second disk drives such that they face each other, wherein the second major faces of the first and second disk drives are each substantially plastic. 
     In some embodiments, the method includes coupling the first disk drive and the second disk drive to the substrate with the first major face of the first disk drive facing with a partial offset the first major face of the second disk drive. In some embodiments, the method includes coupling the first disk drive and the second disk drive to the substrate with the first major face of the first disk drive facing with no offset the first major face of the second disk drive. In some embodiments, the method includes forming a first coupled pair that includes the first and second disk drive, and forming a second coupled pair having a third and fourth disk drive with a first major face of the third disk drive facing with no offset a first major face of the fourth disk drive, and a second major face of the second disk drive facing with partial offset a second major face of the third disk drive. 
     In some embodiments, the method includes installing a controller that receives a disk access request specifying a data length of 2L and based on the request sends substantially simultaneous disk access requests to the first and second disk drive each specifying a data length of L. In some embodiments, the substantially simultaneous disk access request sent to the first and second disk drives cause seek operations having rotational forces that at least partially cancel each other. 
     In some embodiments, the method includes forming the plurality of disk drives into coupled pairs having substantially opposite rotational torque within each pair. In some embodiments, the method includes coupling a first edge of each coupled pair to the substrate and coupling an opposing second edge to an elastomeric material. In some embodiments, the method includes stabilizing at least some of the plurality of disk drives with a stabilizing member having an elastomeric material in contact with the disk drives between the first edge and the second edge of the respective disk drives. In some embodiments, the stabilizer member is a plate member having an elastomeric material in contact with at least some of the plurality of the disk drives between the first edge and the second edge of the respective disk drives. In some embodiments, the plate member is substantially parallel to the first edge of the disk drives and includes a plate having perforations that encircle each disk drive. In some embodiments, the plate member further includes an elastomeric material bridging a gap between an edge of a perforation in the plate member and the disk drive encircled by the perforation. 
     In some embodiments, the method includes orienting the plurality of first disk drives and second disk drives as alternately facing coupled pairs. In some embodiments, for each one of a plurality of disk drives, a first major face of a respective drive is spaced closer to its nearest neighbor&#39;s first major face as compared to the spacing of the respective drive&#39;s second major face to its nearest neighbor&#39;s second major face, the second major faces having lower heat conductivity than the first major faces. In some embodiments, for each one of a plurality of disk drives, a first major face of a respective drive is spaced further from its nearest neighbor&#39;s first major face as compared to the spacing of the respective drive&#39;s second major face to its nearest neighbor&#39;s second major face, the second major faces having lower heat conductivity than the first major faces. 
     In some embodiments, the method includes coupling each of the plurality of first and second disk drives electrically and mechanically to the substrate in a row that conforms to a line, wherein the first disk drives and the second disk drives are alternately positioned within the row as neighboring disk drives. In some embodiments, the row includes two or more disk drives and fewer than about two-hundred-and-one disk drives. In some embodiments, each of the first disk drives have a first major face and a second opposing major face and wherein each of the second disk drives have a first major face and a second opposing major face, and wherein the first major face of each first disk drive faces the first major face of an adjoining second disk drive, and the second major face of each first disk drive faces the second major face of an adjoining second disk drive. In some embodiments, the method includes conforming the row to a substantially linear line. In some embodiments, the method includes conforming the row to a substantially stepped curved line. In some embodiments, the method includes conforming the stepped curved line so that it follows a substantially exponential curve. In some embodiments, the method includes conforming the row to a substantially smooth curved line. In some embodiments, the method includes conforming the substantially smooth curved line so that it curves in a substantially exponential manner. In some embodiments, the method includes positioning the first and second disk drives with a spacing between adjacent drives, wherein the spacing between the neighboring disk drives follows a substantially exponential function. In some embodiments, the method includes adding one or more additional rows of disk drives. In some embodiments, the method includes positioning the rows on the substrate with substantially mirror image orientation relative to an adjoining row. 
     In some embodiments, the method includes elastomerically coupling the disk drives at an edge of each disk drive that is opposite the substrate. In some embodiments, the method includes enclosing the substrate and the disk drives. In some embodiments, the substrate is oriented so that it is substantially parallel to a first major surface of the enclosure. In some embodiments, the method includes providing at least one air inlet along a first surface of the enclosure and at least one air outlet along a second surface of the enclosure. In some embodiments, the method includes adding at least one manifold that directs airflow over the disk drives. In some embodiments, the method includes flowing air through the at least one manifold and between the disk drives. In some embodiments, the method includes adding at least one air-movement device to the enclosure. In some embodiments, the method includes adding one or more pairs of fans that are coupled to have opposite rotational direction. In some embodiments, the method includes providing a cover for the enclosure. In some embodiments, the method includes attaching a resilient material to the cover and to a second edge of each one of a plurality of the disk drives. In some embodiments, the method includes attaching stiffening ribs to the cover. In some embodiments, the method includes adding a shipping-overshock display. In some embodiments, the method includes adding a mother board, a personality board, or any combination thereof. 
     In some embodiments, the invention provides an apparatus that includes an enclosure that includes a substrate, a means in the enclosure for mounting a plurality of disk drives to the enclosure, and a means for coupling a plurality of disk drives electrically and mechanically to the substrate, the plurality of disk drives including at least a first and a second disk drive, and wherein the first disk drive is positioned relative to the second disk drive so that a rotational force produced by the first disk drive is at least partially counteracted by a rotational force produced by the second disk drive. 
     In some embodiments, the invention provides an apparatus that includes a substrate, and a plurality of disk drives each coupled electrically and mechanically to the substrate, the plurality of disk drives including at least a first disk drive and a second disk drive, wherein the first and second disk drive each have a first major face surrounded by a first, second, third and fourth edge and having a first, second, third and fourth corner, wherein the first disk drive and the second disk drive are positioned such that a rotational force produced by the first disk drive is conveyed primarily as a translational force to the second disk drive. In some embodiments, the apparatus includes an enclosure, wherein the substrate and the plurality of disk drives are attached to the enclosure, at least one memory, and an information processing unit operatively coupled to the disk drives and to the memory, wherein the information processing unit sends read commands to the disk drives and receives data from the disk drives and from the memory. In some embodiments, the information processing unit includes a multi-processor supercomputer. 
     In some embodiments, the apparatus includes a plurality of substantially similar enclosures, wherein each enclosure holds a substrate and plurality of disk drives including at least a first disk drive and a second disk drive positioned such that a rotational force produced by the first disk drive is conveyed primarily as a translational force to the second disk drive, and wherein the plurality of enclosures are operatively coupled to the supercomputer. 
     In some embodiments, the apparatus includes a memory, and a video-streaming apparatus operatively coupled to receive data from the memory, wherein the video-streaming apparatus is adapted to transmit digital video to a plurality of destinations and users. 
     In some embodiments, the apparatus includes an enclosure to which the substrate is connected that encloses the substrate and the plurality of disk drives. 
     In some embodiments of the apparatus, the first edge of each of the first and second disk drives includes a substantially neutral position, relative to rotational force, located along the first edge between the first corner and the second corner. In some embodiments, the first disk drive and the second disk drive are positioned relative to each other so that the neutral position of the first disk drive is at a position along the first edge of the first disk drive that is closest to the first corner of the second disk drive. In some embodiments, the first disk drive and the second disk drive are positioned with their first major faces substantially perpendicular to each other. In some embodiments, the first disk drive and the second disk drive are positioned with their first major faces at an acute angle. In some embodiments, the first disk drive and the second disk drive are positioned with their first major faces substantially parallel to each other. In some embodiments, the first disk drive and the second disk drive are positioned with their first major faces laterally offset from each other. 
     In some embodiments, the apparatus includes an air-deflection vane positioned to direct additional air between the first disk drive and the second disk drive. 
     In some embodiments of the apparatus, the first disk drive and the second disk drive are positioned such that a rotational force produced by the second disk drive is at least partially conveyed as a translational force to the first disk drive. In some embodiments, the first disk drive and the second disk drive are positioned such that the rotational force produced by the second disk drive is conveyed primarily as a translational force to the first disk drive. In some embodiments, the first disk drive and the second disk drive are positioned such that the rotational force produced by the first disk drive is conveyed only as a translational force to the second disk drive. In some embodiments, the first disk drive and the second disk drive are positioned such that the rotational force produced by the second disk drive is conveyed only as a translational force to the first disk drive. 
     In some embodiments of the apparatus, the first disk drive has a disk rotational torque vector due to its rotating disk(s) that is substantially antiparallel to a disk rotational torque vector of the second disk drive that is due to its rotating disk(s). In some embodiments, the first disk drive and the second disk drive are positioned with their first major faces laterally offset from each other. 
     In some embodiments of the apparatus, the first disk drive has a disk rotational torque vector due to its rotating disk(s) that is substantially coparallel (i.e., that is collinear or parallel) to a disk rotational torque vector of the second disk drive that is due to its rotating disk(s). In some embodiments, the first disk drive and the second disk drive are positioned with their first major faces laterally offset from each other. 
     In some embodiments, the apparatus includes a resilient boot unit coupled between the first edge of each of the plurality of drives and the substrate. In some embodiments, the resilient boot unit includes a visco-elastic polymer material. In some embodiments, the resilient boot unit includes an elastomeric polymer material. In some embodiments, the apparatus includes one or more resilient materials between at least some of the plurality of disk drives and the substrate. In some embodiments, the resilient material has graded shock absorbance characteristics. In some embodiments, the resilient material includes a visco-elastic material. In some embodiments, the resilient material includes a vibration damping polymer. 
     In some embodiments, the apparatus includes a cover plate, and a resilient cap coupled between the second edge of each of the plurality of drives and the cover plate, wherein the second edge is on an opposite side of the first major face from the first edge. In some embodiments, the resilient cap includes a visco-elastic polymer material. In some embodiments, the resilient cap includes an elastomeric polymer material. In some embodiments, the resilient cap is adhesively coupled to the second edge of at least some of the plurality of disk drives. In some embodiments, the resilient boot unit is adhesively coupled to the first edge of at least some of the plurality of disk drives. 
     In some embodiments of the apparatus, the enclosure includes at least one air-inlet manifold and at least one air-outlet manifold, wherein air substantially passes from the inlet manifold between the first disk drive and second disk drive to the outlet manifold. In some embodiments, the apparatus includes at least one manifold that directs airflow over the disk drives. In some embodiments, the apparatus includes an air-movement device. In some embodiments, the air-movement device includes one or more fans. In some embodiments, the air-movement device includes at least one pair of fans that are mechanically coupled and have opposite rotation directions. 
     The invention provides a method that includes mounting a plurality of disk drives in an enclosure, the plurality of disk drives including at least a first disk drive and a second disk drive that are each electrically and mechanically coupled to the enclosure, and mechanically coupling the first disk drive and the second disk drive such that rotational force produced by the first disk drive is at least partially transmitted as translational force to the second disk drive. In some embodiments, the method includes operatively coupling an information processing unit to the enclosure, and adding a memory to the enclosure, wherein the information processing unit is operatively coupled to the disk drives and to the memory, and wherein the information processing unit sends read commands to the disk drives and receives data from the disk drives and memory. In some embodiments, the method includes utilizing a multi-processor supercomputer as the information processing unit. In some embodiments, the method includes operatively coupling a plurality of substantially similar enclosures to the supercomputer, wherein each enclosure holds a substrate and plurality of disk drives including at least a first disk drive and a second disk drive positioned such that a rotational force produced by the first disk drive is conveyed primarily as a translational force to the second disk drive, and wherein the plurality of enclosures are operatively coupled. In some embodiments, the method includes operatively coupling a memory to the enclosure, and operatively coupling a video-streaming apparatus to the enclosure, wherein the video-streaming apparatus receives data from the memory and is adapted to transmit digital video to a plurality of destinations and users. 
     In some embodiments, the method includes performing a seek function with the first disk drive, wherein a rotational force is produced. 
     In some embodiments, the method includes positioning the first disk drive and the second disk drive relative to each other so that a neutral position of the first disk drive is positioned along a first edge of the first disk drive that is closest to a first corner of the second disk drive. In some embodiments, the method includes positioning the first disk drive and the second disk drive with their first major faces substantially perpendicular to each other. In some embodiments, the method includes positioning the first disk drive and the second disk drive with their first major faces at an acute angle to each other. In some embodiments, the method includes positioning the first disk drive and the second disk drive with their first major faces substantially parallel to each other. In some embodiments, the method includes positioning the first disk drive and the second disk drive with their first major faces laterally offset from each other. 
     In some embodiments, the method includes positioning an air-deflection vane to direct additional air between the first disk drive and the second disk drive. 
     In some embodiments, the method includes positioning the first disk drive and the second disk drive such that a rotational force produced by the second disk drive is at least partially conveyed as a translational force to the first disk drive. In some embodiments, the method includes positioning the first disk drive and the second disk drive such that the rotational force produced by the second disk drive is substantially conveyed as a translational force to the first disk drive. In some embodiments, the method includes positioning the first disk drive and the second disk drive such that the rotational force produced by the first disk drive is conveyed only as a translational force to the second disk drive. In some embodiments, the method includes positioning the first disk drive and the second disk drive such that the rotational force produced by the second disk drive is conveyed only as a translational force to the first disk drive. In some embodiments, the method includes positioning the first disk drive so that a disk rotational torque vector due to its rotating disk(s) is substantially antiparallel to a disk rotational torque vector of the second disk drive that is due to its rotating disk(s). In some embodiments, the method of claim  5 , further including positioning the first disk drive and the second disk drive with their first major faces laterally offset from each other. 
     In some embodiments, the method includes positioning the first disk drive so that a disk rotational torque vector due to its rotating disk(s) is substantially coparallel to a disk rotational torque vector of the second disk drive that is due to its rotating disk(s). In some embodiments, the method includes positioning the first disk drive and the second disk drive with their first major faces laterally offset from each other. In some embodiments, the method includes damping relative motion between at least some of the plurality of disk drives and the substrate. In some embodiments, the method includes using one or more resilient materials to dampen vibration energy. In some embodiments, the method includes using one or more resilient materials having graded shock absorbance characteristics. In some embodiments, the method includes using one or more resilient materials that include a vibration damping polymer. In some embodiments, the method includes using one or more resilient materials that include a visco-elastic material. In some embodiments, the method includes coupling a resilient boot unit between the first edge of each of the plurality of drives and the substrate. In some embodiments, the method includes using a resilient boot unit that includes a visco-elastic polymer material. In some embodiments, the method includes using a resilient boot unit that includes an elastomeric polymer material. 
     In some embodiments, the method includes adding a cover plate, and coupling a resilient cap between the second edge of each of the plurality of drives and the cover plate. In some embodiments, the method includes using a resilient cap that includes a visco-elastic polymer material. In some embodiments, the method includes using a resilient cap that includes an elastomeric polymer material. In some embodiments, the method includes adhesively coupling the resilient cap to the second edge of at least some of the plurality of disk drives. In some embodiments, the method includes adhesively coupling the resilient boot unit to the first edge of at least some of the plurality of disk drives. 
     The invention provides an apparatus that includes a substrate, and a means for mounting a plurality of disk drives to the substrate, and a means for coupling a plurality of disk drives electrically and mechanically to the substrate, the plurality of disk drives including at least a first disk drive and a second disk drive, wherein the first and second disk drive each have a first major face surrounded by a first, second, third and fourth edge and having a first, second, third and fourth corner, wherein the first disk drive and the second disk drive are positioned such that a rotational force produced by the first disk drive is conveyed primarily as a translational force to the second disk drive. 
     The invention provides an apparatus that includes a substrate, and a plurality of disk-drive connectors each coupled electrically and mechanically to the substrate, the plurality of disk-drive connectors including at least a first and a second disk-drive connector, wherein the first disk-drive connector is positioned relative to the second disk-drive connector so that a rotational force produced by a first disk drive that is connected to the first disk-drive connector is at least partially counteracted by a rotational force produced by a second disk drive that is connected to the second disk-drive connector. In some embodiments, the apparatus includes an enclosure, wherein the substrate and the plurality of disk-drive connectors are attached to the enclosure, at least one memory, and an information processing unit operatively coupled to the disk-drive connectors and to the memory, wherein the information processing unit sends read commands to disk drives that are connected to the disk-drive connectors and receives data from the disk drives and from the memory. In some embodiments, the information processing unit includes a multi-processor supercomputer. In some embodiments, the apparatus includes a plurality of substantially similar enclosures, wherein each enclosure holds a substrate and plurality of disk-drive connectors including at least a first disk-drive connector and a second disk-drive connector positioned such that a rotational force produced by a first disk drive that is connected to the first disk-drive connector is conveyed primarily as a translational force to a second disk drive that is connected to the second disk-drive connector, and wherein the plurality of enclosures are operatively coupled to the supercomputer. In some embodiments, the apparatus includes a memory, and a video-streaming apparatus operatively coupled to receive data from the memory, wherein the video-streaming apparatus is adapted to transmit digital video to a plurality of destinations and users. 
     In some embodiments of the apparatus, the plurality of disk-drive connectors includes more than two first disk-drive connectors in a first rotating orientation and fewer than about one-hundred-and-one first disk-drive connectors, and a substantially equal number of second disk-drive connectors in a second counter rotating orientation, wherein a plurality of the first and a plurality of the second disk-drive connectors are interleaved in coupled pairs. In some embodiments, the plurality of disk-drive connectors includes more than about one-hundred first disk-drive connectors and fewer than about two-hundred-and-one first disk-drive connectors, and a substantially equal number of second disk-drive connectors, wherein a plurality of the first and a plurality of the second disk-drive connectors are interleaved in coupled pairs so that first disk drives connected to the first disk-drive connectors each rotate in one orientation and the second disk drives connected to the second disk-drive connectors rotate in a counter orientation. In some embodiments of the apparatus, at least some of the plurality of disk-drive connectors are each in contact with a boot unit. In some embodiments, the boot unit includes one or more resilient materials. In some embodiments, the boot unit has graded shock absorbance characteristics. In some embodiments, the boot unit includes a vibration damping polymer. In some embodiments, the boot unit includes a visco-elastic material. In some embodiments of the apparatus, at least a portion of each one of the plurality of disk-drive connectors is adhesively connected to its boot unit. In some embodiments, of the apparatus, at least a portion of each one of the plurality of disk-drive connectors is bonded to its boot unit. 
     In some embodiments, the apparatus includes a detent device adapted to be placed in disengageable contact with each one of a plurality of disk drives that are connected to each one of the disk-drive connectors, wherein the detent device contacts the disk drive at an edge distal from the disk drive&#39;s first edge. In some embodiments, the detent device is wedge shaped at a first end and adapted to be inserted against each of a plurality of disk drives that are inserted into the disk-drive connectors, wherein the detent device can be used for transport and disengaged for disk drive operation. In some embodiments, the detent device includes a cam mechanism adapted to be engaged for transport and disengaged for operation of disk drives that are connected to each of the disk-drive connectors. 
     In some embodiments of the apparatus, the first disk-drive connector is positioned so that a first disk drive that is connected to the first disk-drive connector has a disk rotational torque vector due to its rotating disk(s) that is substantially antiparallel to a disk rotational torque vector that is due to a rotating disk(s) of a second disk drive that is connected to the second disk-drive connector. In some embodiments of the apparatus, the disk rotational torque vector of the first disk drive that is connected to the first disk-drive connector is substantially collinear with the disk rotational torque vector of the second disk drive that is connected to the second disk-drive connector. In some embodiments of the apparatus, the disk rotational torque vector of the first disk drive that is mounted in the first disk-drive connector is radially offset from the disk rotational torque vector of the second disk drive that is connected to the second disk-drive connector. In some embodiments of the apparatus, the actuator rotational torque vector due to actuator arm rotation in a first disk drive that is mounted in the first disk-drive connector is substantially collinear with the actuator rotational torque vector of a second disk drive that is connected to the second disk-drive connector. In some embodiments of the apparatus, the first disk-drive connector and the second disk-drive connector are coupled to the substrate so that a first disk drive connected to the first disk-drive connector is oriented with a first major face of the first disk drive facing with a partial offset a first major face of a second disk drive that is mounted in the second disk-drive connector. In some embodiments, the first disk-drive connector and the second disk-drive connector are coupled to the substrate so that a first disk drive connected to the first disk-drive connector is oriented with a first major face of the first disk drive facing with no offset a first major face of a second disk drive that is mounted in the second disk-drive connector. In some embodiments, the first and second disk-drive connectors form a first coupled pair, further comprising a second coupled pair having a third and fourth disk-drive connector, wherein the disk-drive connectors are positioned so that a first major face of a third disk drive connected to the third disk-drive connector faces with no offset a first major face of a fourth disk drive that is connected to the fourth disk-drive connector, and a second major face of a second disk drive that is connected to the second disk-drive connector faces with partial offset a second major face of the third disk drive that is connected to the third disk-drive connector. 
     In some embodiments, the apparatus includes a controller that receives a disk access request specifying a data length of 2L and based on the request sends substantially simultaneous disk access requests to a first and second disk drive that each specify a data length of L, wherein the first and second disk drive are each connected to a first and second disk-drive connector. In some embodiments, the substantially simultaneous disk access request sent to the first and second disk drives cause seek operations having rotational forces that at least partially cancel each other. 
     In some embodiments of the apparatus, the plurality of disk-drive connectors are formed into coupled pairs so that disk drives connected to the disk-drive connectors have substantially opposite rotational torque within each pair. In some embodiments, a portion of each coupled pair of disk-drive connectors is coupled to the substrate and a portion of each disk-drive connector is coupled to an elastomeric material. 
     In some embodiments, the apparatus includes a stabilizer member having an elastomeric material in contact with at least a portion of the disk-drive connectors. In some embodiments, the stabilizer member is a plate member having an elastomeric material in contact with at least a portion of the disk-drive connectors. 
     In some embodiments of the apparatus, the plurality of first disk drive and second disk-drive connectors are oriented as alternately facing coupled pairs. In some embodiments, the plurality of disk-drive connectors are positioned as a first pair of disk-drive connectors that include first and second disk-drive connectors and a second pair of disk-drive connectors that include third and fourth disk-drive connectors on the substrate, wherein a space between the first and second disk-drive connectors is less than a space between the first and second pairs of disk-drive connectors. 
     In some embodiments of the apparatus, the plurality of first and second disk-drive connectors are each coupled electrically and mechanically to the substrate in a row that conforms to a line, wherein the first disk-drive connectors and the second disk-drive connectors are facing in alternate directions positioned within the row. In some embodiments, the row includes two or more disk-drive connectors and fewer than two-hundred-and-one disk-drive connectors. In some embodiments, the row conforms to a substantially linear line. In some embodiments, the row conforms to a substantially stepped curved line. In some embodiments, the stepped curved line curves in a substantially exponential manner. In some embodiments, the row conforms to a substantially smooth curved line. In some embodiments, the substantially smooth curved line curves in a substantially exponential manner. 
     In some embodiments, the apparatus includes one or more additional rows of disk-drive connectors. In some embodiments, the rows are positioned on the substrate with substantially mirror image orientation relative to a neighboring row. 
     In some embodiments, the apparatus includes an enclosure. In some embodiments, the substrate is oriented parallel to a first major surface of the enclosure. In some embodiments, the enclosure includes at least one air inlet and at least one air outlet. In some embodiments, the apparatus includes at least one manifold that directs airflow over disk drives when they are connected to the disk-drive connectors. In some embodiments, the apparatus includes an air-movement device. In some embodiments, the air-movement device includes one or more fans. In some embodiments, the air-movement device includes one or more pairs of fans that rotate in opposite directions. In some embodiments, the enclosure includes a cover. In some embodiments, the cover includes a resilient material. In some embodiments, a resilient material is attached to the cover. In some embodiments, the cover includes at least one stiffening rib. In some embodiments, the apparatus includes a resilient material that is attached to a second edge of each one of a plurality of disk drives that are connected to the disk-drive connectors. In some embodiments, the apparatus includes a shipping-overshock display. In some embodiments, the apparatus includes a mother board, a personality board, or any combination thereof. 
     The invention provides an apparatus that includes a substrate, and a plurality of disk-drive connectors each coupled electrically and mechanically to the substrate, the plurality of disk-drive connectors including at least a first disk-drive connector and a second disk-drive connector, wherein the first disk-drive connector and the second disk-drive connector are positioned such that a rotational force produced by a first disk drive connected to the first disk-drive connector is conveyed primarily as a translational force to a second disk drive connected to the second disk-drive connector. In some embodiments, the apparatus includes an enclosure, wherein the substrate and the plurality of disk-drive connectors are attached to the enclosure, at least one memory, and an information processing unit operatively coupled to disk drives that are connected to the disk-drive connectors and to the memory, wherein the information processing unit sends read commands to the disk drives and receives data from the disk drives and from the memory. In some embodiments, the information processing unit includes a multi-processor supercomputer. 
     In some embodiments, the apparatus includes a plurality of substantially similar enclosures, wherein each enclosure holds a substrate and plurality of disk-drive connectors including at least a first disk-drive connector and a second disk-drive connector that are positioned such that a rotational force produced by a first disk drive connected to the first disk-drive connector is conveyed primarily as a translational force to a second disk drive that is connected to the second disk-drive connector, and wherein the plurality of enclosures are operatively coupled to the supercomputer. 
     In some embodiments, the apparatus includes a memory, and a video-streaming apparatus operatively coupled to receive data from the memory, wherein the video-streaming apparatus is adapted to transmit digital video to a plurality of destinations and users. 
     In some embodiments, the apparatus includes an enclosure to which the substrate is connected that encloses the substrate and a plurality of disk drives that are connected to the plurality of disk-drive connectors. 
     In some embodiments of the apparatus, the disk-drive connectors are positioned so that a first edge of each of a first and second disk drive that are connected to the disk-drive connectors includes a substantially neutral position, relative to rotational force, located along the first edge between the first corner and the second corner of the disk drive. In some embodiments, the first disk-drive connector and the second disk-drive connector are positioned relative to each other so that the neutral position of a first disk drive connected to the first disk-drive connector is at a position along the first edge of a first disk drive that is closest to the first corner of a second disk drive that is connected to the second disk-drive connector. In some embodiments, the first disk-drive connector and the second disk-drive connector are positioned so that a first and second disk drives connected to the first and second disk-drive connectors are positioned with their first major faces substantially perpendicular to each other. In some embodiments, the first disk-drive connector and the second disk-drive connector are positioned so that a first disk drive connected to the first disk-drive connector and a second disk drive connected to the second disk-drive connector are positioned with their first major faces at an acute angle. In some embodiments, the first disk-drive connector and the second disk-drive connector are positioned so that a first disk drive connected to the first disk-drive connector and a second disk drive connected to the second disk-drive connector are positioned with their first major faces substantially parallel to each other. In some embodiments, the first disk-drive connector and the second disk-drive connector are positioned so that a first disk drive connected to the first disk-drive connector and a second disk drive connected to the second disk-drive connector are positioned with their first major faces laterally offset from each other. In some embodiments, the first disk-drive connector and the second disk-drive connector are also positioned such that a rotational force produced by a second disk drive that is connected to the second disk-drive connector is at least partially conveyed as a translational force to a first disk drive that is connected to the first disk-drive connector. In some embodiments, the first disk-drive connector and the second disk-drive connector are also positioned such that the rotational force produced by a second disk drive that is connected to the second disk-drive connector is conveyed primarily as a translational force to a first disk drive that is connected to a first disk-drive connector. In some embodiments, the first disk-drive connector and the second disk-drive connector are also positioned such that a rotational force produced by a first disk drive that is connected to a first disk drive is conveyed only as a translational force to a second disk drive that is connected to the second disk-drive connector. In some embodiments, the first disk-drive connector and the second disk-drive connector are also positioned such that a rotational force produced by a second disk drive that is connected to the second disk-drive connector is conveyed only as a translational force to a first disk drive that is connected to the first disk-drive connector. 
     In some embodiments of the apparatus, the first disk drive has a disk rotational torque vector due to its rotating disk(s) that is substantially antiparallel to a disk rotational torque vector of the second disk drive that is due to its rotating disk(s). In some embodiments, the first disk-drive connector and the second disk-drive connector are positioned so that a first disk drive that is connected to the first disk-drive connector and a second disk drive that is connected to the second disk-drive connector are positioned with their first major faces laterally offset from each other. In some embodiments, the first disk-drive connector and the second disk-drive connector are positioned so that a first disk drive that is connected to the first disk-drive connector has a disk rotational torque vector due to its rotating disk(s) that is substantially coparallel to a disk rotational torque vector due to a rotating disk(s) of a second disk drive that is connected to the second disk-drive connector. In some embodiments, the first disk-drive connector and the second disk-drive connector are positioned so that a first disk drive that is connected to the first disk-drive connector and a second disk drive that is connected with the second disk-drive connector have their first major faces laterally offset from each other. 
     In some embodiments, the apparatus includes one or more resilient materials between at least some of the plurality of disk-drive connectors and the substrate. In some embodiments, the resilient material has graded shock absorbance characteristics. In some embodiments, the resilient material includes a visco-elastic material. In some embodiments, the resilient material includes a vibration damping polymer. 
     In some embodiments, the apparatus includes an enclosure that includes at least one air-inlet manifold and at least one air-outlet manifold, wherein air substantially passes from the inlet manifold between a first disk drive that is connected to the first disk-drive connector and a second disk drive that is connected to the second disk-drive connector to the outlet manifold. 
     In some embodiments, the apparatus includes an air-movement device. In some embodiments, the air-movement device includes one or more fans. In some embodiments, the air-movement device includes at least one pair of fans that are mechanically coupled and have opposite rotation directions. 
     The invention provides a method that includes mounting a plurality of disk-drive connectors in an enclosure, the enclosure including a connector substrate, the plurality of disk-drive connectors including at least a first disk-drive connector and a second disk-drive connector that are each electrically and mechanically coupled to the enclosure, and mechanically coupling the first disk-drive connector and the second disk-drive connector such that rotational force produced by a first disk drive that is connected to the first disk-drive connector is at least partially counteracted by rotational force produced by a second disk drive that is connected to the second disk-drive connector. 
     In some embodiments, the method includes operatively coupling an information processing unit to the enclosure, and adding a memory to the enclosure, wherein the information processing unit is operatively coupled to disk drives that are connected to the disk-drive connectors and to the memory, wherein the information processing unit sends read commands to the disk drives and receives data from the disk drives and memory. In some embodiments, the method includes utilizing a multi-processor supercomputer as the information processing unit. 
     In some embodiments, the method includes operatively coupling a plurality of substantially similar enclosures to the supercomputer, wherein each enclosure holds a substrate and plurality of disk-drive connectors including at least a first disk-drive connector and a second disk-drive connector positioned such that a rotational force produced by a first disk drive that is connected to the first disk-drive connector is conveyed primarily as a translational force to a second disk drive that is connected to the second disk-drive connector, and wherein the plurality of enclosures are operatively coupled. 
     In some embodiments, the method includes operatively coupling a memory to the enclosure, and operatively coupling a video-streaming apparatus to the enclosure, wherein the video-streaming apparatus receives data from the memory and is adapted to transmit digital video to a plurality of destinations and users. 
     In some embodiments, the method includes positioning the plurality of disk-drive connectors such that a number of the first disk-drive connectors, the number being greater than two and fewer than about one-hundred-and-one, are in a first orientation, and a substantially equal number of second disk-drive connectors are in a second orientation, wherein a plurality of first disk drives and second disk drives that are connected to the first and second disk-drive connectors are interleaved in mechanically coupled pairs with opposite rotating orientation. In some embodiments, the method includes positioning the first disk-drive connector so that a disk rotational torque vector due to a rotating disk(s) of a first disk drive that is connected to the first disk-drive connector is substantially antiparallel to a disk rotational torque vector of a second disk drive that is due to a rotating disk(s) of a second disk drive that is connected to the second disk-drive connector. In some embodiments, the method includes positioning the first disk-drive connector so that a disk rotational torque vector due to a rotating disk(s) of a first disk drive that is connected to the first disk-drive connector is substantially collinear to a disk rotational torque vector of a second disk drive that is due to a rotating disk(s) of a second disk drive that is connected to the second disk-drive connector. In some embodiments, the method includes positioning the first disk-drive connector so that a disk rotational torque vector due to a rotating disk(s) of a first disk drive that is connected to the first disk-drive connector is radially offset to a disk rotational torque vector of a second disk drive that is due to a rotating disk(s) of a second disk drive that is connected to the second disk-drive connector. In some embodiments, the method includes positioning the first disk-drive connector so that a disk rotational torque vector due to a rotating disk(s) of a first disk drive that is connected to the first disk-drive connector is collinear to a disk rotational torque vector of a second disk drive that is due to a rotating disk(s) of a second disk drive that is connected to the second disk-drive connector. In some embodiments, the method includes coupling the first disk-drive connector and the second disk-drive connector to the substrate so that a first major face of a first disk drive connected to the first disk-drive connector faces with a partial offset of a first major face of a second disk drive that is connected to the second disk-drive connector. In some embodiments, the method includes coupling the first disk-drive connector and the second disk-drive connector to the substrate so that a first major face of a first disk drive connected to the first disk-drive connector faces with no offset of a first major face of a second disk drive that is connected to the second disk-drive connector. In some embodiments, the method includes forming a first coupled pair that includes the first and second disk-drive connector, and forming a second coupled pair having a third and fourth disk-drive connector so that a first major face of a third disk drive that is connected to the third disk-drive connector faces with no offset a first major face of a fourth disk drive that is connected to the fourth disk-drive connector, and a second major face of a second disk drive that is connected to the second disk-drive connector faces with partial offset a second major face of the third disk drive. 
     In some embodiments, the method includes installing a controller that receives a disk access request specifying a data length of 2L and based on the request sends substantially simultaneous disk access requests specifying a data length of L a first and second disk drive that are connected to the first and second disk-drive connectors. In some embodiments of the method, the substantially simultaneous disk access request sent to the first and second disk drives cause seek operations having rotational forces that at least partially cancel each other. 
     In some embodiments, the method includes forming the plurality of disk-drive connectors into coupled pairs so that disk drives connected to the disk-drive connectors have substantially opposite rotational torque within each pair of disk drives. In some embodiments, the method includes orienting the plurality of first disk-drive connectors and second disk-drive connectors so that first disk drives and second disk drives connected to the first and second disk-drive connectors form alternately facing coupled pairs. In some embodiments, the method includes coupling each of the plurality of first and second disk-drive connectors electrically and mechanically to the substrate in a row that conforms to a line, wherein first and second disk drives that are connected to the first and second disk-drive connectors are alternately positioned within the row as neighboring disk drives. In some embodiments, the row includes two or more disk-drive connectors and fewer than about two-hundred-and-one disk-drive connectors. In some embodiments, the method includes conforming the row to a substantially linear line. In some embodiments, the method includes conforming the row to a substantially stepped curved line. In some embodiments, the method includes conforming the stepped curved line so that it follows a substantially exponential curve. In some embodiments, the method includes conforming the row to a substantially smooth curved line. In some embodiments, the method includes conforming the substantially smooth curved line so that it curves in a substantially exponential manner. In some embodiments, the method includes positioning the first and second disk-drive connectors with a spacing between adjacent disk-drive connectors, wherein the spacing between neighboring disk-drive connectors follows a substantially exponential function. In some embodiments, the method includes adding one or more additional rows of disk-drive connectors. In some embodiments, the method includes positioning the rows on the substrate with substantially mirror image orientation relative to an adjoining row. 
     In some embodiments, the method includes enclosing the substrate and disk-drive connectors in an enclosure. In some embodiments, the method includes orienting the substrate so that it is substantially parallel to a first major surface of the enclosure. In some embodiments, the method includes providing at least one air inlet along a first surface of the enclosure and at least one air outlet along a second surface of the enclosure. In some embodiments, the method includes adding at least one manifold that directs airflow over the disk-drive connectors. In some embodiments, the method includes adding at least one air-movement device to the enclosure. In some embodiments, the method includes adding one or more pairs of fans that are coupled to have opposite rotational direction. 
     In some embodiments, the method includes providing a cover for the enclosure. In some embodiments, the method includes attaching stiffening ribs to the cover. In some embodiments, the method includes adding a shipping-overshock display. In some embodiments, the method includes adding a mother board, a personality board, or any combination thereof. 
     In some embodiments, the invention provides an apparatus that includes an enclosure for holding a plurality of drives in each of one or more rows including a first row, a plurality of sockets arranged along the first row with the socket&#39;s long dimensions generally parallel to one another and at a non-parallel angle to the first row, each socket providing electrical connection and mechanical support along a first connector edge of one or more disk drives, and a resilient support member adapted to hold a second edge other than the first connector edge of each disk drive, such that the enclosure forms an inlet air manifold along a first side of the first row and an outlet air manifold along an opposite second side of the first row. 
     In some embodiments of the apparatus, the inlet air manifold has a length measured parallel to the first row that is longer than the inlet air manifold&#39;s width measured perpendicular to the first row, and wherein the outlet air manifold has a length measured parallel to the first row that is longer than the outlet air manifold&#39;s width measured perpendicular to the first row. 
     In some embodiments of the apparatus, the sockets for the first row are mounted to circuit board forming an internal plane of the enclosure, and wherein the resilient support member includes a cover mounted parallel to the circuit board. 
     In some embodiments of the apparatus, the cover includes a sheet-metal plate and a visco-elastic material that is located between the plate and each disk drive position, the visco-elastic material adapted to adhere to the cover and to each disk drive. 
     Some embodiments of the apparatus further include a plurality of disk drives mounted to the enclosure. 
     In some embodiments, the invention provides a method that includes mounting a plurality of disk-drive connectors in an enclosure, the plurality of disk-drive connectors including at least a first disk-drive connector and a second disk-drive connector that are each electrically and mechanically coupled to the enclosure, and mechanically coupling the first disk-drive connector and the second disk-drive connector such that rotational force produced by a first disk drive that is connected to the first disk-drive connector is at least partially transmitted as translational force to a second disk drive that is connected to the second disk-drive connector. 
     In some embodiments, the method includes operatively coupling an information processing unit to the enclosure, and adding a memory to the enclosure, wherein the information processing unit is operatively coupled to disk drives that are connected to the disk-drive connectors and to the memory, and wherein the information processing unit sends read commands to the disk drives and receives data from the disk drives and memory. In some embodiments, the method includes utilizing a multi-processor supercomputer as the information processing unit. 
     In some embodiments, the method includes operatively coupling a memory to the enclosure, and operatively coupling a video-streaming apparatus to the enclosure, wherein the video-streaming apparatus receives data from the memory and is adapted to transmit digital video to a plurality of destinations and users. 
     In some embodiments, the method includes positioning the first disk-drive connector and the second disk-drive connector relative to each other so that a neutral position of the first disk drive that is connected to the first disk-drive connector is at a position along the first edge of the first disk drive that is closest to a first corner of a second disk drive that is connected to the second disk-drive connector. In some embodiments, the method includes positioning the first disk-drive connector and the second disk-drive connector so that a first disk drive connected to the first disk-drive connector and a second disk drive connected to the second disk-drive connector are positioned with their first major faces substantially perpendicular to each other. In some embodiments, the method includes positioning the first disk-drive connector and the second disk-drive connector so that a first disk drive connected to the first disk-drive connector and a second disk drive connected to the second disk-drive connector are positioned with their first major faces at an acute angle. In some embodiments, the method includes positioning the first disk-drive connector and the second disk-drive connector so that a first disk drive connected to the first disk-drive connector and a second disk drive connected to the second disk-drive connector are positioned with their first major faces substantially parallel to each other. In some embodiments, the method includes positioning the first disk-drive connector and the second disk-drive connector so that a first disk drive connected to the first disk-drive connector and a second disk drive connected to the second disk-drive connector are positioned with their first major faces laterally offset from each other. 
     In some embodiments, the method includes positioning an air-deflection vane to direct additional air between a first disk drive and a second disk drive that are connected to the first disk-drive connector and the second disk-drive connector. 
     In some embodiments, the method includes positioning the first disk-drive connector and the second disk-drive connector such that a rotational force produced by a second disk drive that is connected to the second disk-drive connector is at least partially conveyed as a translational force to a first disk drive that is connected to the first disk-drive connector. In some embodiments, the method includes positioning the first disk-drive connector and the second disk-drive connector such that a rotational force produced by a second disk drive that is connected to the second disk-drive connector is substantially conveyed as a translational force to a first disk drive that is connected to the first disk-drive connector. In some embodiments, the method includes positioning the first disk-drive connector and the second disk-drive connector such that a rotational force produced by a second disk drive that is connected to the second disk-drive connector is conveyed only as a translational force to a first disk drive that is connected to the first disk-drive connector. In some embodiments, the method includes positioning the first disk-drive connector and the second disk-drive connector so that a disk rotational torque vector due to a rotating disk(s) of a first disk drive connected to the first disk-drive connector is substantially antiparallel to a disk rotational torque vector that is due to a rotating disk(s) of a second disk drive that is connected to the second disk-drive connector. In some embodiments, the method includes positioning the first disk-drive connector and the second disk-drive connector so that a first major face of a first disk drive that is connected to the first disk-drive connector is laterally offset from a first major face of a second disk drive that is connected to the second disk-drive connector. 
     In some embodiments, the method includes positioning the first disk-drive connector and the second disk-drive connector so that a disk rotational torque vector due to a rotating disk(s) of a first disk drive connected to the first disk-drive connector is substantially coparallel to a disk rotational torque vector that is due to a rotating disk(s) of a second disk drive that is connected to the second disk-drive connector. In some embodiments, the method includes positioning the first disk-drive connector and the second disk-drive connector so that a first major face of a first disk drive that is connected to the first disk-drive connector is laterally offset from a first major face of a second disk drive that is connected to the second disk-drive connector. 
     In some embodiments, the method includes damping relative motion between at least some of the plurality of disk drives that are connected to the plurality of disk-drive connectors and the substrate. In some embodiments, the method includes using one or more resilient materials to dampen vibration energy. In some embodiments, the method includes using one or more resilient materials having graded shock absorbance characteristics. In some embodiments, the method includes using one or more resilient materials that include a vibration damping polymer. In some embodiments, the method includes using one or more resilient materials that include a visco-elastic material. 
     The invention provides a method that includes mounting a plurality of disk drives in an enclosure, the enclosure including a connector substrate, the plurality of disk drives including at least a first disk drive and a second disk drive, vibrationally coupling the first disk drive to the second disk drive, and sending a first seek operation to the first disk drive and a second seek operation to the second disk drive, wherein a timing of the first seek operation relative to the second seek operation is adjusted to minimize adverse vibrational interaction between the first disk drive and the second disk drive. 
     In some embodiments, the method includes mechanically coupling the first disk drive and the second disk drive such that rotational force produced by the first disk drive is at least partially counteracted by rotational force produced by the second disk drive. In some embodiments, the first and second seek operations are performed substantially simultaneously. In some embodiments, the first and second seek operations are timed so that the second seek operation does not occur while the first disk drive is reading data. In some embodiments, the first and second seek operations are timed so that the second seek operation does not occur while the first disk drive is writing data. 
     In some embodiments, the method includes obtaining vibration-interaction information regarding the first and second disk drives and adjusting the time of the second seek operation based on the information. In some embodiments, the method includes performing a plurality of seek operations to the second disk drive while the first disk drive is reading data in order to generate the vibration-interaction information. In some embodiments, the method includes storing the vibration interaction information in a look-up table. 
     In some embodiments of the method, the plurality of disk drives further include a third disk drive and a fourth disk drive and the method further includes performing a plurality of seek operations to the third disk drive while the first disk drive is reading data in order to generate vibration-interaction information relating to the third and first disk drives, storing the vibration interaction information in the look-up table, and choosing between performing a seek operation to the second disk drive versus performing a seek operation to the third disk drive based on the vibration-interaction information contained in the look-up table. 
     The invention provides an apparatus that includes a data structure having a plurality of entries, each entry containing vibration-interaction information relative to a read operation occurring on a first disk drive of a pair of disk drives and a seek operation being performed on a second disk drive of the pair. In some embodiments, the apparatus includes a memory and an information processing unit operatively coupled together, wherein the data structure is stored in the memory and wherein the information processing unit is adapted to adjust a timing of at least one seek operation based on information stored in the data structure. In some embodiments, the apparatus includes a video-streaming unit operatively coupled to the information processing unit, wherein the video-streaming unit receives data from the memory and is adapted to transmit digital video to a plurality of destinations and users. In some embodiments, the apparatus includes a multi-processor supercomputer operatively coupled to the information processing unit. 
     The invention provides an apparatus that includes a memory, the memory holding vibration-interaction information, and an information processing unit operatively coupled to the memory to receive the vibration-interaction information and adjust a timing of seek operations to a plurality of disk drives based on the information. In some embodiments, the apparatus includes an enclosure that holds the plurality of disk drives, the enclosure operatively coupled to the information-processing unit. 
     The invention provides a method that includes mounting a plurality of disk drives in shock mounts in an enclosure, and detenting the plurality of disk drives against vibration using a disengagable detent device. In some embodiments of the method, the detenting includes inserting a disengagable detent device that is wedge shaped at a first end and adapted to be inserted against each of a plurality of disk drives for transport and which can be disengaged for disk operation. In some embodiments, the inserting includes wedging the detent device against a plurality of disk drives in a non-simultaneous sequential manner. In some embodiments, the detenting includes camming a disengagable detent device into an engaged position for shipping; wherein the detent device is adapted to be disengaged for disk drive operation. In some embodiments, the camming is performed against a plurality of disk drives in a non-simultaneous sequential manner. In some embodiments, the camming is performed against a plurality of disk drives in a substantially simultaneous manner. 
     The invention provides an apparatus that includes an enclosure, a substrate held within the enclosure, a plurality of disk-drive connectors each coupled mechanically to the substrate, the plurality of disk-drive connectors including at least a first and a second disk-drive connector, and an over-shock detector operatively coupled to the enclosure and adapted to detect and store information regarding one or more over-shock events. In some embodiments, the apparatus includes at least one boot unit that includes one or more resilient materials, wherein at least some of the plurality of disk-drive connectors are each in contact with a boot unit. In some embodiments, the apparatus includes at least one boot unit having graded shock absorbance characteristics. In some embodiments, the apparatus includes at least one boot unit that includes a vibration damping polymer. In some embodiments of the apparatus, the over-shock detector is further operable to store time information regarding the over-shock events. 
     The invention provides a method that includes analyzing vibration-interaction between a plurality of disk drives held in an enclosure, and storing information that is based on the analysis into a data structure. In some embodiments, the method includes reading the stored information and adjusting a timing of at least one seek operation based on the information. 
     The invention provides a method that includes mounting a plurality of disk drives to disk-drive connectors within an enclosure, adhering a resilient sheet across the plurality of disk drives, and attaching a cover to the resilient sheet. In some embodiments of the method, attaching of the cover further includes adhering the cover to the resilient sheet. In some embodiments, the resilient sheet is attached to the cover before the resilient sheet is adhered to the plurality of disk drives. In some embodiments, the method includes connecting each of the plurality of disk drives to a boot unit. In some embodiments, the method includes adjusting a height of the boot unit based on a vibration characteristic of the plurality of disk drives. In some embodiments, the method includes connecting each of the plurality of disk drives to its own respective boot unit. In some embodiments, the method includes connecting each of the plurality of disk drives to a plurality of boot units. In some embodiments, the method includes connecting each of the plurality of disk drives to a vibration-absorbing member. In some embodiments, the method includes adjusting a height of the vibration-absorbing member based on a vibration characteristic of the plurality of disk drives. In some embodiments, the method includes connecting each of the plurality of disk drives to its own respective vibration-absorbing member. In some embodiments, the method includes connecting each of the plurality of disk drives to a plurality of vibration-absorbing members. 
     The invention provides an apparatus that includes a plurality of disk drives mounted to disk-drive connectors within an enclosure, a resilient sheet across the plurality of disk drives, and a cover. In some embodiments, the cover is adhered to the resilient sheet. In some embodiments, the resilient sheet is attached to the cover before the resilient sheet is adhered to the plurality of disk drives. In some embodiments, each of the plurality of disk drives is connected to a boot unit. In some embodiments, a height of the boot unit is adjusted based on a vibration characteristic of the plurality of disk drives. In some embodiments, each of the plurality of disk drives is connected to its own respective boot unit. In some embodiments, each of the plurality of disk drives is connected to a plurality of boot units. In some embodiments, each of the plurality of disk drives is connected to a vibration-absorbing member. In some embodiments, a height of the vibration-absorbing member is adjusted based on a vibration characteristic of the plurality of disk drives. In some embodiments, each of the plurality of disk drives is connected to its own respective vibration-absorbing member. In some embodiments, each of the plurality of disk drives is connected to a plurality of vibration-absorbing members. 
     It is to be understood that the above description is intended to be illustrative, and not restrictive. Although numerous characteristics and advantages of various embodiments as described herein have been set forth in the foregoing description, together with details of the structure and function of various embodiments, many other embodiments and changes to details will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should be, therefore, determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein,” respectively. Moreover, the terms “first,” “second,” and “third,” etc., are used merely as labels, and are not intended to impose numerical requirements on their objects.