Patent Publication Number: US-2006010275-A1

Title: Removable disk storage array emulating tape library having backup and archive capability

Description:
FIELD OF THE INVENTION  
      The present invention relates to methods and apparatus for protecting user data within a computer system. More specifically, the present invention relates to a removable rotating disk drive data storage array for emulating tape library functions including backing up and archiving user data.  
     BACKGROUND OF THE INVENTION  
      The need for effective and reliable backup and archive of user data information is well known. Considerable information system (IS) resources are devoted to providing backup and archive of information resident in computers and servers within any organization that produces and/or relies upon digital information.  
      The term “backup” means that periodically, such as each day, a backup record is made which mirrors then-present information content of computer active memory embodied as semiconductor random access memory, and/or a hard disk drive or drives, of a computer or computer server. This backup operation usually, although not necessarily, involves a transfer to magnetic tape and occurs during a period of likely minimum usage of the underlying data storage resource, such as in the middle of the night. If the storage resource is thereafter lost or becomes unavailable on account of equipment failure, or for any other reason, it is then possible to use the backup record to reconstruct the state of the information in storage as of the last backup time and date.  
      The daily backup procedure may be followed by a weekly backup procedure, a monthly backup procedure, a quarterly backup procedure, and so forth. At any point in the backup procedure, selected backup data storage media, frequently backup tape cartridges, may be physically removed from the system and relocated to a secure storage location away from the information processing/storage center. Secured backup tape cartridges then function as archival tape cartridges. One drawback of archival tape cartridges is that once they are removed to the secure storage site, they become presently unavailable to the computing system; and, depending upon conditions such as temperature, humidity, handling and storage conditions within the storage site, the tape/cartridge may deteriorate or degrade. If later needed, the archived user digital data information on the tape media of such cartridges may turn out to be unavailable.  
      One procedure which is used to safeguard data integrity of data on archive tape cartridges is to remove each cartridge periodically from the secure storage site, load each cartridge into a tape drive and unspool and respool the reeled tape, by carrying out an operation known as “repacking the tape pancake”. During this tape-spooling operation, some or all of the archive data may be read out to determine whether such data remains intact and available as an archive. If the tape media is determined to be deteriorating, as measured by error correction activity for example, a replacement archive tape cartridge may be loaded and the archived data on the failing tape cartridge may then be transferred to the replacement cartridge. Then, the failing tape cartridge can then be discarded. Such procedures tend to be time consuming, labor-intensive, and evidently expensive. Repeated handling and use of a tape cartridge shortens its useful life and can directly lead to its failure as a data archive resource.  
      One further drawback of tape archiving methods and technology is that drive transports are being constantly improved and upgraded technologically. It has proven very difficult to provide backwards-compatibility in tape archive systems such that more recent tape drives are able to read and recover user data from older tapes using less dense data recording formats, all other considerations being the same.  
      One other drawback of tape archiving methods has arisen during efforts to re-use archive tapes because of less than complete erasure of overwritten data. This problem has led some users to treat tape cartridges as one-use devices, greatly adding to the expense of tape archive systems operations and management. Also, because the tape cartridge is not a sealed system, external contaminants and influences may prevent a tape transport mechanism from successfully reading an archive tape. Further, tape cartridge handling equipment including tape transports, tend to be very complicated electro-mechanical structures, with multiple tape path control loops and other interactive tape handling processes. If any one of these processes fails or degrades, the tape may be damaged or destroyed. Moreover, tapes written on one tape transport may not be readable on another tape transport because of accumulation of head-tape alignment errors.  
      Tape recording has evolved since its earliest beginnings over forty years ago. Large reels of open tape have given way to small compact tape cartridges that hold increasing quantities of magnetic storage tape capable of being recorded with ever-greater information density. One form of compact single reel cartridge tape is the streaming digital linear tape system marketed by the assignee of the present invention under the DLT™ brand. The DLT system includes individual tape drives, as well as tape cartridge handling equipment and libraries. Recently, it has been proposed to create a virtual tape library by using a single DLT tape device, or several such devices within a cartridge loader environment. An example of this virtual tape library is found in commonly assigned U.S. Pat. No. 6,067,481 to Saliba, entitled: “Virtual Magnetic Tape Drive Library System”. An example of a cartridge loader environment is found in commonly assigned U.S. Pat. No. 5,760,995 to Heller et al., entitled: “Multi-Drive, Multi-Magazine Mass Storage and Retrieval Unit for Tape Cartridges. The disclosures of U.S. Pat. Nos. 6,067,481 and 5,760,995 are incorporated herein by reference thereto.  
      Cartridge media libraries, whether tape or optical, are well known in the art, and frequently comprise “walls of cartridges” or large cylindrical cartridge bin arrangements. A so-called “picker-gripper” mechanism (robot) operating under computer control accesses a particular cartridge bin, grips the cartridge media unit present, withdraws it from the bin, translates it to a media drive unit and causes the cartridge media unit to be loaded into the drive unit in a predetermined way. One example of an optical storage and retrieval device comprising a wall of optical media cartridges is disclosed in U.S. Pat. No. 4,675,856 to Rudy et al, entitled: “Optical Storage and Retrieval Device”, the disclosure thereof being incorporated herein by reference.  
      Over the past forty years tape storage has been perceived to be a less expensive method for providing off-line storage than disk drives. While tape media alone may be somewhat less expensive than equivalent rotating hard disk drive storage, when a complex electromechanical tape drive is included, the comparison becomes more equivalent. As the rotating hard disk drive storage cost-per-information-unit continues to drop, the storage industry is beginning to shift its paradigm for backup, to other storage systems, such as rotating hard disk drives.  
      Currently, optical and low-density magnetic media (e.g.: Iomega ZIP™ drive system) are seen as alternatives to tape backup and archive. The Linear Tape Open (LTO) Consortium is offering an alternative to streaming digital linear tape (DLT).  
      Moreover, it has been proposed to emulate tape systems and libraries with hard disk drive arrays by using a variety of technologies known as “virtual tape”. Virtual tape makes disk drive resources appear as if they are sequentially accessed tape drives. By using disk drive subsystems as virtual tape devices, it is possible to stream backup data at very high data rates over a storage application network (SAN). Thus, for applications and computing environments requiring higher-speed backup devices and processes, for example on the order of 40 Mbytes per second or faster, virtual tape may provide the necessary data throughput.  
      Computer storage systems providers such as IBM, Sun Microsystems, Storage Technology Corporation, and EMC 2  Corporation, offer large hard disk drive array products which may be configured as virtual tape libraries, but which do not exactly mirror or correspond to DLT tape backup/archive systems. Examples of prior art virtual tape devices and systems are found in U.S. Pat. No. 4,467,421 to White, entitled: “Virtual Storage System and Method”; U.S. Pat. No. 5,963,971 to Fosler et al., entitled: “Method and Apparatus for Handling Audit Requests of Logical Volumes in a Virtual Media Server”; U.S. Pat. No. 6,049,848 to Yates et al., entitled: “System and Method for Performing High-Speed Tape Positioning Operations”; U.S. Pat. No. 6,070,224 to LeCrone et al., entitled: “Virtual Tape System”; U.S. Pat. No. 6,098,148 to Carlson, entitled: “Storage and Access of Data Using Volume Trailer”; and, U.S. Pat. No. 6,105,037 to Kishi, entitled: “Apparatus for Performing Automated Reconcile Control in a Virtual Tape System”. The disclosures of these patents are incorporated herein by reference. These prior disclosures fail to provide any teaching or suggestion that the disk drives or disk drive arrays performing the virtual tape drive emulation can be physically removed from an active data store and relocated to a secure data archive location and then provide the archive function typically performed by removable archive tape media.  
      Rotating hard disk drives are known to be susceptible to, and can be damaged by, sharp shock forces incident to handling. Such forces may cause the hard ceramic head sliders to deform the relatively soft aluminum alloy disk substrate. Accordingly, while tape storage has been emulated by disk storage, rotating hard disk drives are generally more fragile than tape cartridges from a media handling perspective.  
      Removable hard disk drive systems are known in the prior art. One example of such a system previously offered for sale by the assignee of the present invention under the “Passport™ brand is described inter alia in U.S. Pat. No. 5,253,129 to Blackborow et al., entitled: “Removable and Transportable Hard Disk Subsystem”. That system and patent describes a hard disk drive module which was loaded into, and thereupon electrically connected with, a base housing unit, which was in turn connected electrically to a host computer via a bus structure. A hard disk drive was shock-mounted inside of a metal cartridge to provide primary resistance to shock forces. A shock-resistant carrying case provided further shock resistance to the hard disk drive cartridge and enabled the cartridge to be safely transported and stored in a secure, shock-resistant environment. The Passport product found particular acceptance within the national security field where it is necessary to lock up hard disk drives containing data embodying national secrets or classified information in safes and secure areas at night or during periods of inattention. An improvement in the original “Passport” removable hard disk technology is found in U.S. Pat. No. 5,297,067 to Blackborow et al., entitled: “Electronic Hot Connection of Disk Drive Module to Computer Peripheral Bus”. The &#39;067 patent describes methods and apparatus enabling a standard hard disk drive unit to be “hot” connected and disconnected via a standard peripheral bus interface, such as SCSI, with an associated computing system.  
      An expansible fixed disk drive data storage subsystem which enables attachment of a variable number of bus-level-interface hard disk drives at a single bus level logical address location is described in U.S. Pat. No. 5,097,439 to Patriquin et al., entitled: “Expansible Fixed Disk Drive Subsystem for Computer”, the disclosure of which is incorporated herein by reference. A rotating hard disk drive array employing redundant array of individual disks (RAID) formed on hot-pluggable circuit cards is described in Statutory Invention Registration No. H1221 to Best et al., entitled: “High Speed Small Diameter Disk Storage System”, the disclosure thereof being incorporated herein by reference.  
      The disclosures of U.S. Pat. Nos. 5,253,129, 5,297,067, 5,097,439 and Statutory Registration H1221 fail to describe or suggest a removable multi-drive hard disk drive system for providing not only high speed backup in a real-time computing environment, but also being separately capable of being removed to a different operating environment for providing data archival storage, periodic integrity checking and reduced bandwidth retrieval without any further physical relocation or handling of the particular drives and multi-drive modules.  
      Therefore, a hitherto unsolved need has remained for a removable hard disk storage array capable of emulating tape library backup and archive functions in a manner overcoming limitations and drawbacks of the prior art.  
     OBJECTS OF THE INVENTION  
      A general object of the present invention is to provide a computer-network-attached rotating hard disk storage backup and archive system which emulates tape storage backup and archive systems and which is scalable from an entry level system to an enterprise system in a manner overcoming limitations and drawbacks of the prior art.  
      A more specific object of the present invention is to realize vastly improved tape storage backup and archive system functionality with performance, reliability and cost advantages of hard disk drive technology in a network-attached storage system.  
      Yet another specific object of the present invention is to provide a data storage backup and archive library which does not require operator intervention or robots in order to move a tape cartridge between a storage bin and a tape transport with a cartridge handler mechanism, thus overcoming limitations and drawbacks of prior tape cartridge handling solutions associated with cartridge loaders and tape libraries. In fact, one object of the present invention is to eliminate the cartridge media transport mechanism entirely.  
      One more specific object of the present invention is to provide a network-accessible data storage backup and archive library system in which removable magazines of hard disk drives emulate magazines of removable tape cartridges.  
      Yet another specific object of the present invention is to implement a storage system comprising a wall of multiple rotating hard disk drives in a manner analogous to a wall of tape cartridges, yet without need for separate tape drives and robotic tape cartridge handling apparatus or other externally moving parts or components.  
      One more specific object of the present invention is to provide a magazine of hard disk drives which may be installed and used in a high speed, high bandwidth data storage rack electrically coupled to a high performance computer, and which may be removed to, installed in and electrically accessed at a data archive rack monitored by a supervisory controller and connected to the high performance computer via a lower bandwidth network connection.  
      Yet another object of the present invention is to implement a unique file mark structure for implementing tape file marks within logical block address space of a hard disk drive emulating a tape cartridge.  
      These and other objects, advantages, aspects and features of the present invention will be more fully understood and appreciated upon consideration of the following detailed description of preferred embodiments presented in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      In the Drawings:  
       FIG. 1  is an isometric view of a storage rack or bay for holding and connecting two seven-drive rotating hard disk unit magazines in accordance with principles of the present invention.  
       FIG. 2A  is an isometric view of a rack-mounted storage bay for holding and connecting two fourteen-drive rotating hard disk unit magazines in accordance with principles of the present invention.  
       FIG. 2B  is a highly diagrammatic, isometric view of the  FIG. 2A  storage bay and magazines, illustrating flow of cooling air across individual drive units.  
       FIG. 3A  is a highly diagrammatic top plan view and block diagram of one embodiment of a multi-drive magazine of the type shown in  FIG. 1 , illustrating a serial ATA drive interface within an active computing environment.  
       FIG. 3B  is a highly diagrammatic top plan view and block diagram showing the  FIG. 3A  magazine within an inactive data preservation environment, in accordance with principles of the present invention.  
       FIG. 4A  is a highly diagrammatic top plan view and block diagram of a second embodiment of a multi-drive magazine of the type shown in  FIG. 1 , illustrating a USB parallel bridge interface within an active computing environment.  
       FIG. 4B  is a highly diagrammatic top plan view and block diagram showing the  FIG. 4A  magazine within an inactive data preservation environment.  
       FIG. 5  is a highly diagrammatic top plan view and block diagram of a third embodiment of a multi-drive magazine of the type shown in  FIG. 1 , illustrating a 1394 Standard computer interface architecture.  
       FIG. 6A  is a top plan view of a multi-drive magazine of the type shown in  FIG. 1 , illustrating shock mounting.  
       FIG. 6B  is an isometric view of a magazine foam shock mount of the type employed in the  FIG. 6A  embodiment.  
       FIG. 7  is an electrical block diagram of a removable hard disk storage system comprising an array of multi-drive magazines for emulation of high transfer rate tape library backup functions within a central computing environment.  
       FIG. 8  is an electrical block diagram of a removable hard disk storage system of the type shown in  FIG. 7  wherein a SCSI bus architecture is employed within the central computing environment.  
       FIG. 9  is an isometric view of an active hard disk data storage system comprising a series of racks holding a multiplicity of hard drive magazines and showing air ventilation paths and means.  
       FIG. 10  is an isometric view of a shock-insulated transport case for transporting up to two multi-drive magazines from the central computing environment to a secure archive environment at a remote site.  
       FIG. 11  is an isometric view of an off-line archival storage rack system for receiving a multiplicity of multi-drive hard disk magazines and for connecting each magazine to a drive monitoring system.  
       FIG. 12  is a diagrammatic top plan view of the  FIG. 11  off-line archival storage rack system.  
       FIG. 13  is a flowchart illustrating operation of the  FIG. 11  off-line archival storage rack system in accordance with principles of the present invention.  
       FIG. 14  is a diagram mapping logical block address space of a hard disk drive to storage space of a tape cartridge, showing placement of double linked file mark data structures.  
       FIG. 15  is a table illustrating structure of a file mark shown in the  FIG. 14  diagram. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
      As noted above, hard disk drives have a number of advantages over tape cartridges for backing up and archiving computer data. Hard disk drives are fully enclosed and are generally less sensitive to changes in environmental conditions, such as temperature and humidity. Hard disk drives have data storage capacities, which closely approach storage capacities of tape cartridges. Moreover, given the susceptibility to damage incident to periodic handling and repacking of the tape pancake, tape cartridges may have average useful life less than hard disk drive units. In one aspect of the present invention, hard disk drive units are installed into multi-drive magazines. The magazines plug into active storage racks of a high speed, high bandwidth data storage array of an active computing system such as a mainframe, or a network server. The drives are operated in parallel and provide high-speed random storage and access for data files. The drives may be kept in the active environment for a number of months or years. During the period of active disk drive usage, each of the drives will be fully tested and proven to be serviceable. Once a nominal useful life of the drives of a magazine is reached, such as 3-5 years, the magazine can be transitioned to a data archive unit. Data to be archived is then recorded onto the drives of the magazine, and it is then removed from active service, transported in a suitable shock protection carrier, and reinstalled in a drive monitoring rack in an archive location. Then, on a periodic schedule, each drive is powered up and checked in turn, to be sure that it continues to function properly and provides nominal read/write functionality. The drive&#39;s prognostics are monitored and measured against a degradation profile. If a drive is determined to be failing, then a flag is set and the magazine and drive can be removed and replaced. If the data is striped across the multiple drives of the module in a known manner, the drive monitoring system may be able to reconstruct the data of the failed drive. Alternatively, a relatively low bandwidth path may exist between the active computing system and the archive system, and the active host computer may be able to reconstruct the data from the failed drive and return it to a replacement drive installed in the magazine, or in another magazine. Also, it is practical for the host computing system to retrieve archive data from the archive system via the limited bandwidth connection, thereby eliminating any requirement that the drive/magazine be handled or transported. Further advantages and features of the present invention will become even more apparent from considering the following descriptions, which accompany the drawings.  
      Glossary of Terms Used  
     
         
          ARCHIVAL MAGAZINE: A removable shock-protected storage unit for mounting and connecting a predetermined number of self-contained rotating hard disk drive units, such as 7 or 14 such units.  
          DATA PRESERVATION VAULT: A system of interconnected racks for receiving and connecting archival magazines and drive units. The vault may be co-located with an active computing system, or it may be located at a different site, such as a location made to be secure from hazards such as fire, floods, earthquake, storms, etc.  
          ATA: An acronym for “advanced technology attachment”, representing a hard disk drive industry standard interface providing 100 Megabyte per second low cost parallel interface.  
          BRIDGE BOARD: A printed circuit board containing electronic circuitry to interconnect between a particular hard disk drive unit and one or more system interfaces.  
          DISK MONITORING SYSTEM: An arrangement of hardware and software for monitoring on a periodic basis all hard disk drive units of magazines installed in the Data Preservation Vault.  
          IEEE 1394: An industry standard 320 Megabit per second serial small computer system interface (SCSI) structure and convention.  
          SERIAL ATA: An industry-proposed fast serial interface for ATA interface hard disk drive units.  
          USB 2.0: An industry standard 480-Megabit per second universal serial bus interface structure and convention.  
          ACTIVE DATA STORAGE ARRAY: An on-line data storage/backup system containing one to a multiplicity of Archival Magazines.  
       
    
      Having in mind the foregoing, components of a removable disk storage array  10  incorporating principles of the present invention are shown in the  FIG. 1  depiction. Therein, a rack-mountable storage bay, or cabinet,  12  is sized to define a plurality of wells  13  and an electronic backplane circuit board  15 . In the present example, left and right wells  13  are defined within cabinet  12  to receive two hard disk drive magazines  14 A and  14 B. In  FIG. 1  magazine  14 A is shown removed from the left well  13 , and in front of the cabinet  12 , while magazine  14 B is shown in the installed position fully within the right interior well  13  of the cabinet  12 . Each magazine  14  has a standardized external physical layout arrangement (“form factor”), and may include such handling features, such as one or more handles  16  enabling an operator to grasp the magazine  14  in order to install it into a particular well  13  of cabinet  12 . Most preferably, the act of installing a magazine  14  into a well  13  of cabinet  12  simultaneously accomplishes a task of connecting the magazine to electrical power supply and one or more computer data interface connector structure  17  which is part of or co-located with the backplane circuit board  15 . Such an arrangement may be followed to facilitate “hot connection” or “hot swap” of magazines within the cabinet  12  in a manner described in U.S. Pat. No. 5,297,067 or Statutory Invention Registration H1221, referred to hereinabove. The magazine bay  12  is most preferably of a standardized height and a standardized width, such as 19 inches, so that it may be installed in a conventional mainframe computer equipment rack. The bay  12  is generally open at the top and bottom, so that airflow streams may be directed between the drives  20 , e.g., from bottom to top as shown by the bold arrows of the  FIG. 1  example.  
      Each magazine  14  most preferably includes a predetermined number of hard disk drive units  20 . In the  FIG. 1  example, each magazine  14 A,  14 B holds e.g., seven (7) hard disk drive units  20 A,  20 B,  20 C,  20 D,  20 E,  20 F,  20 G. In the  FIG. 2A  example, each magazine  14 C,  14 D holds e.g. up to 14 hard disk drive units  20 A,  20 B,  20 C,  20 D,  20 E,  20 F,  20 G,  20 H,  20 I,  20 J,  20 K,  20 L,  20 M, and  20 N. Shock-resistant formed-foam mounts  21 , shown in  FIG. 6 , are provided within each magazine  14 , so that shock forces generated during normal handling of the magazine  14  during installation and removal to and from the bay  12  do not damage the delicate internal components of the hard disk drive units. Each hard disk drive unit  20  most preferably has an industry-standardized form factor, such as 3.5-inch disk diameter, half height; 2.5 inch; 1.8 inch; or 1 inch nominal disk diameter, for example. Each drive unit  20  is fully self-contained, offers specified predetermined data storage capacity and average data access time, and includes an industry-standardized interface structure and convention, such as ATA, SCSI or 1394. Ideally, each hard disk drive unit  20  provides 10 Gigabytes, or more, of data storage, and most preferably 30 Gigabytes to 200 Gigabytes or more, which equals or exceeds a contemporary data backup tape cartridge having a similar external form factor.  
      The hard disk drive units  20  are mounted in the magazine  14  with a slightly spaced-apart arrangement. This arrangement enables forced airflow to pass between the units and thereby cool the units  20  and backplane circuit  15  during active use, when the units operate in parallel and generate substantial heat which must be carried off or dissipated. Standard cabling (not shown) is provided to provide power and data connections between each drive unit  20  and a connector structure of each magazine which mates with the connector structure  17  of the bay  12 .  
      As shown in  FIG. 3A , for example, each of the seven hard disk drive units  20 A- 20 G is provided with a visual indicator  22 A- 22 G, such as a light emitting diode (LED). In the  FIG. 3A  example, the LED units  22 A- 22 G are mounted in a transverse lip of the magazine  14 A above a front wall of each drive unit  20 . In the  FIG. 2A  example, the magazines  14 C and  14 D have front panels  23 , which include the 14 visual indicator LEDs  22 A- 22 N, corresponding to drive units  20 A- 20 N respectively. Each LED  22  may be multi-colored, so that one color, such as green, is emitted when the drive unit is operating normally, and another color, such as red, is emitted to indicate a fault condition within the particular drive unit  20 . An amber color may be emitted if a particular drive is failing or degrading, but has not yet failed in service. Information about a variety of operational parameters within a particular unit  20  is typically self-collected and recorded in a reserved section of disk storage space and is available to be read from the unit in order to predict unit failure in accordance with conventional failure prediction methods. These measurements may be of the type described in U.S. Pat. No. 6,122,131 to Jeppson, entitled: “Adaptively-controlled Disk Drive Assembly”, the disclosure thereof being incorporated by reference. A method for predicting early head crashes is described in U.S. Pat. No. 5,410,439 to Egbert et al., entitled: “Disk File with Clearance and Glide Measurement and Early Head Crash Warning”, the disclosure thereof being incorporated herein by reference. Since standard hard disk drive units  20  no longer are equipped with activity lights, the visual indicators  22  are arranged as part of magazine  14  so as to be readily visible to an operator facing the front of the magazine  14 .  
      As shown in  FIGS. 1, 3A ,  4 A and  5 , the drive units  20  are most preferably mounted together within a magazine  14  in a closely-spaced-apart side-by-side arrangement that provides an air-space  24  between adjacently facing major sidewalls of adjacent drive units  20 , thereby admitting an airflow for cooling, as perhaps best shown in  FIG. 2B . Cooling fans  101  at the top of magazine racks  102  of an active backup storage system  100  ( FIG. 9 ) pull air from the ambient through the racks  102  and magazines  14  in order to achieve the desired cooling airflow. This provides the needed cooling of the drive units  20  when they are simultaneously operating and functioning in the active computing environment.  
      In the active computing environment  100  depicted in  FIG. 3A , the magazine  14 A includes, in addition to the seven drives  20 A- 20 G a series of internal serial buses  32  and serial connectors  34  in number equal to the number of drive units  20  present. In this present example, serial buses  32 A,  32 B,  32 C,  32 D,  32 E,  32 F and  32 G respectively connect serial ATA interfaces of drive units  20 A,  20 B,  20 C,  20 D,  20 E,  20 F, and  20 G to serial connectors  34 A,  34 B,  34 C,  34 D,  34 E,  34 F and  34 G of the magazine  14 A. These connectors  34 A- 34 G respectively mate with serial bus connectors  36 A- 36 G of the bay  20  (as part of connector structure  17  shown in FIGS.  1  and  2 A). A set of Serial ATA Host controllers  38 A- 38 G may be respectively connected to connectors  36 A- 36 G. The controllers  38 A- 38 G then connect to a SCSI target circuit  40 , which connects via a suitable SCSI bus  42  to a SCSI host  50  within a host computing system. Each magazine  14  may be provided with a unique identifier, such as bar code pattern readable by a conventional bar code scanning system, and/or an electrical identifier such as an embedded serial number readable by the control circuitry  15  of a particular bay  20 . Alternatively, each disk drive  20 , or the magazine  14 , or the bay  12 , may include an internet protocol (IP) address in accordance with the internet data transfer protocol, TCP/IP. An optically readable identifier is preferably provided so that the identity of a particular magazine may be established during transit or storage and without need to plug the particular magazine  14  into a bay  12 . The reader may be included as a part of the bay  12 , or the reader may additionally or alternatively be a hand held unit of conventional design and function.  
      Power is most preferably supplied to each drive unit  20  in parallel from a high efficiency 48V to 5V/12V DC to DC switching converter circuit  44  located within the magazine  14 A. The converter  44  derives its operating power through a magazine power connector  46  which mates with a bay power connector  48  connected to a DC power supply providing sufficient power to operate all seven of the drives  20  simultaneously. Drive operating power may be switched on at each drive unit  20  under software control from the host  50 . Individual drive unit power switching is illustrated in  FIG. 3A  by a power command register/switch circuit  49 , there being seven such circuits  49 A,  49 B,  49 C,  49 D,  49 E,  49 F, and  49 G associated respectively with drive units  20 A- 20 G.  
      Once archive data is written onto disk drive units  20  within a magazine  14  at an active storage system  100 , the magazine  14  may be removed and reinstalled at a bay within a rack of the data preservation vault.  FIG. 3B  illustrates a data preservation vault  300 , which includes a drive monitoring system  304 . The drive monitoring system  304  includes compatible data and power plug connectors, which mate with, like connectors of the magazine  14 . In the example of  FIG. 3B , serial ATA connectors  318 A,  318 B,  318 C,  318 D,  318 E,  318 F,  318 G mate respectively with connectors  34 A- 34 G of magazine  14 . A power connector  320  mates with power connector  46  of magazine  14 . Since only one disk drive unit  20  will be powered at any time in the archive vault  300 , the power connector  320  may have a smaller power handling capacity than the connector  48  of the active system  100 . The drive monitoring system  304  includes a control line  322  for controlling a switch within the power connector  320  for selectively applying power to the DC to DC converter  44 . Power to be applied to a particular drive is most preferably handled by drive unit commands sent from the drive monitoring system  304  to a particular drive unit  20  via the serial ATA bus structure.  
       FIG. 4A  illustrates an active data storage array  100 A employing drive units in accordance with the USB 2.0 interface convention. A drive magazine  14 E holds seven USB drives  20 P,  20 Q,  20 R,  20 S,  20 T,  20 U and  20 V. The magazine  14 E includes seven USB interface connectors  34 P,  34 Q,  34 R,  34 S,  34 T,  34 U, and  34 V which respectively connect to drive units  20 P- 20 V. The active unit  100 A includes USB connectors  36 P- 36 V which mate with magazine connectors  34 P- 34 V, respectively. Seven USB host controllers  38 P- 38 V are located between connectors  36  and the SCSI target  40 . The SCSI target  40  connects to the SCSI host computing environment  50  via a high speed (2560 Mb/second) bus  42 .  
       FIG. 4B  illustrates a data preservation vault  300 A for use with USB 2.0 magazine  14 E. In this example, connectors  324 P- 324 V mate with connectors  34 P- 34 V and also to a USB hub circuit  326 . The USB hub connects to a USB controller  328 . The USB controller  328  connects too the drive monitoring system  304  via a lower speed bus structure  330  (operating in this example at 480 Mb/second). Otherwise, the  FIG. 4A-4B  system is the same as the  FIG. 3A-3B  system. Alternatively, each magazine  14  may is include the USB hub  326  internally and provide a single USB connection to the SCSI target controller  114  for concentrating and distributing data from and to each drive unit  20 , as shown in the  FIG. 8  arrangement, discussed below.  
      It is not necessary that the hard disk drive units be ATA or serial USB drives. For example,  FIG. 5  illustrates seven interface type 1394 hard disk drive units  20 W,  20 X,  20 Y,  20 Z,  20 AA,  20 BB,  20 CC installed within an interface type 1394 magazine  14 F. With the type 1394 interface convention, the interface bus of drives  20 W- 20 CC may employ a single data bus  32 W which is daisy-chained to all of the drive units and ultimately leads to a type 1394 magazine connector  34 W arranged to mate with a bay type 1394 connector  36 W. While individual magazines  14  and magazine bays  12  may be provided for each interface type, a universal plug-jack interconnection system may be provided in accordance with known techniques, thereby to enable a magazine  14  to be used with disk drive sets of diverse interface conventions.  
       FIGS. 6A and 6B  illustrate a shock mounting arrangement for use within the drive unit magazine  14 . Therein, formed-foam shock absorbers  21  are placed between an outer frame of the magazine  14  and a bundle comprising the side-by-side mounted hard disk drive units  20 . Each shock absorber  21  may be formed to define a series of nested rectangular spaces and openings adapted to fit closely over an outermost disk drive unit  20 A or  20 G, and provide an air passage to improve ventilation and cooling of the nested disk drive unit.  
      Turning now to  FIG. 7 , a computing center active disk drive system  100  includes a multiplicity of hot-swap bays  12  of the type shown in  FIGS. 1 and 2 A, and associated HDD magazines  14 , as shown in  FIGS. 3A, 4A  and/or  5 . The system  100  is arranged in a series of large mounting racks  102 , there being five such units  102 A,  102 B,  102 C,  102 D and  102 E shown in the  FIG. 7  example. Dots to the right side of the rack  102 E denote expandability of the system beyond the five racks shown in  FIG. 7 . In addition to the interface subsystem  40  and host computer  50 , the active system  100  may include a main board  102 , an operator display  104 , and a power supply  106 , for controlling the magazines  14  and drives  20 . The power supply  106  provides primary operating power to the main board  102 , controller  40 , display  104  and each drive magazine  14  installed within the array of racks  102 . As configured, the system  100  may provide active data backup as a full emulation of a tape library wherein each drive  20  emulates a separate tape cartridge. Alternatively, the active system  100  may provide a primary random access data store for the host computer  50  and be configured in accordance with RAID or any other known storage system architecture and methodology.  
      Most preferably, the system  100  emulates a tape library system, such as a tape library shown in commonly assigned U.S. Pat. No. 5,925,119 to Maroney, entitled: “Computer Architecture for Automated Storage Library”, the disclosure thereof being incorporated herein by reference. In a virtual tape emulation system  100 , the main board  102  intercepts commands issued to a tape library system and converts tape-library-specific commands such as media load/unload commands into electrical control signals for selecting/spinning up and down of a particular disk drive  20  and tape-file specific commands such as file read or write into logical block based disk-drive-specific commands by which logical block address locations are randomly accessed by the selected drive  20  so that a series of user data block read or write operations are carried out on a tape file structured basis.  
       FIG. 8  illustrates an embodiment  112  of the system  100  within an active computing environment which is configured to include a single SCSI target controller  114  for handling e.g. ten data unit magazines  14 A,  14 B,  14 C,  14 D,  14 E,  14 F,  14 G,  14 H,  14 I, and  14 J. The target controller  114  has a high bandwidth SCSI bus  118  leading to a SCSI host of the active computer system (not shown in  FIG. 8 ). In this particular example, each magazine  14  is attached via a single SCSI port connector to the SCSI target controller  114 , and each drive  20  within each magazine  14  has a SCSI interface.  
       FIG. 10  shows one embodiment of a shock-providing carrying case  200  for transporting magazines  14  from the active computer center to the archive location. The case  200  includes a shock-resistant foam insert  202  that defines one or more wells, there being two wells  204 A and  204 B shown in the  FIG. 10  example. A lid  206  hinged to the case  200  and also having a shock-resistant foam sheet  208  secures magazines  14  placed in wells  204  against shock forces of the type typically encountered in removal to the archive location. A two-part latch mechanism  210 A,  210 B releasably secures the lid  206  to the case  200  in a closed position which causes facing walls of the foam insert  202  and lid sheet  208  to engage the magazines  14  and provide needed shock resistance for transport.  
       FIGS. 11 and 12  illustrate aspects of an archive system  300  that includes one or a series of side-by-side storage racks  302 . The racks  302  may be located in any desired location, and most preferably in a secure archive location, such as a basement, vault, cave, or other location deemed to be secure against known hazards. The racks  302  may be grouped together, or they may be separated and located at otherwise unused areas of a computing center. Because the disk drives  20  in each magazine  14  are inactive for long periods of time, there is no need for level of power supply or ventilation at the data preservation vault  300  that is needed for the racks  102  of the active backup system  100 .  
      The drive monitoring system  304  includes a power supply  306  and connects to each magazine  14  installed in a particular rack  302  to supply power and a bus connection selectively to each drive  20  within a particular magazine  14 , in order to carry out periodic testing and incidental archive data retrieval without requiring any operator intervention. The archive disk monitoring system controller  304  includes data inputs from an array  308  of environmental sensors, such as temperature, humidity, security access, etc. Most preferably, the archive system controller  304  includes a data path  310  extending to a remote operator console. The remote operator console enables the data vault  300  to be remotely accessed and monitored. Also, the channel  310  enables remote access to the archive information stored on one of the drives of one of the magazines of the system  300 , should such real-time access be desired or required.  
       FIG. 13  sets forth a flowchart of one exemplary disk drive monitoring routine  350  carried out by the data archive controller  304 . At a step  352  the controller  304  applies power to one of the drives  20  within a particular magazine  14  in accordance with a master testing list maintained by and within the controller  304 . The power is applied for a predetermined time period, such as three minutes or less, for example. At a step  354 , the controller  304  sends a “run smart test” command to the drive under test. (The “run smart test” command is a host interface command within a superset of commands and enables a host computing system to test the disk drive and receive status information. The disk drive undergoing testing provides status information back to the controller  304 , such as its prognostics record. The controller  304  determines at the step  354  whether the drive undergoing testing passes or fails the smart test routine. If the drive presently being tested passes the smart test, the controller  304  ceases to apply power to the drive at a step  356 . The next test interval for the particular drive passing the smart test is then recorded in the master testing list by the controller  304  at a step  358 , and the testing procedure advances to a next drive on the testing list at a step  360 , resulting in a return to step  352  and a repeat of the testing sequence is carried out for this next drive.  
      If, however, during the initial testing interval established by step  352 , the disk drive undergoing testing fails to pass the smart test, disk drive  20 Z for example, but still provides some functionality, as tested at a step  362 , a stand-by archive drive  20 R is located among the drives and the magazines of the rack  302 , and the archive data on drive  20 Z is transferred to the stand-by drive  20 R during the step  352 . Then, at a step  364  the controller  304  causes the panel lamp  22 Z of the failed drive  20 Z to flash in a manner indicating failure of the particular drive. At step  364  a message is also sent to the operator console to alert an attendant that an archive drive has failed and needs to be replaced within a particular magazine. The controller  304  then updates the archive records at a step  366  to reflect that the archive data once present on failed drive  20 Z has been transferred to stand-by archive disk drive  20 R.  
      If the failed drive  20 Z loses all functionality, the controller  304  generates a message (step  368 ) based on its archive database to the host active system, indicating that the drive  20 Z has completely failed. This message is most preferably sent via modem  308  and communications channel  310 . The host computer may then be able to reconstitute the data lost on drive Z by resort to error correction techniques associated with data striping across multiple drives. In this regard, the host computer may request the archive system  300  to retrieve user data stripes and error correction overhead from other drives present within the array  300  and transmit that data in serial stream fashion to the host over channel  310 . The host, then applying its error correction/recovery capability then reconstructs the data once held on drive z and sends that data over the channel  310  to a second stand-by drive  20 RR, thereby completing the restoration of data within the archive array  300 .  
      In one aspect of the present invention, each hard disk drive  20  may emulate a tape cartridge. In this aspect of the invention a disk drive will record “tape marks” or “file marks” which would normally be recorded onto tape by a tape drive. “File marks” represent overhead information (metadata) sent by the host to be written on tape to mark a boundary or partition, typically between files or volumes of user data information. In the present invention, file marks and other metadata intended to be recorded on a tape are actually written to a particular hard disk drive  20 . One presently preferred arrangement is shown in  FIG. 14 . Therein, a logical block address space  400  of a hard disk drive  20  is mapped to file space of a virtual tape media, including a beginning-of-media (BOM) mark  402 , and an end-of-media (EOM) mark  404 . The BOM mark  402  corresponds to a logical block address zero (1ba0), while the EOM mark  404  corresponds to a maximum logical block address (max1ba). Between the BOM mark  402  and EOM mark  404  are a series of file marks, four such file marks  406 ,  408 ,  410  and  412  being illustrated in the  FIG. 14  example. Each file mark  406 ,  408 ,  410  and  412  has a separate logical block address.  
      In use the host computer will issue a command that a master file mark be written to the media (which the host believes is tape, for example) The active system controller  106  causes the master file mark to be written outside of user logical block address space. On ATA disk drives  20  of the type discussed in connection with  FIGS. 3A and 3B , the master file mark is written to one of 32 host-vendor-specific SMART log sectors. On SCSI/FibreChannel disk drives, of the type shown in  FIG. 5 , the master file mark is written to the Client Application log page, for example. When a WRITE FILE MARK command is received by the main board  102 , it will cause a selected drive to write a file mark structure at a current logical block address and update previous file mark data structures to include the address of the latest file mark just written. As shown in  FIG. 14 , the file marks  406 ,  408 ,  410 ,  412 , etc., are written across logical block address space in a linked manner most preferably comprising a double linked list heuristic. As shown in  FIG. 15 , the file mark block structure is recorded in its own separate LBA sector of 512 bytes, for example. The file mark record structure includes a title field (“FILEMARK”), a major version field, a minor version field, a partition number, a byte of flag/validity bits, a previous File Mark LBA, a next File Mark LBA, block size, reserved bytes, and two bytes of check sum, for example.  
      When the host computing system “loads” a virtual cartridge in the active backup system  100 , a particular disk  20  drive is selected and reads the master file mark in its reserved space. It then traverses the file mark linked list and stores all file mark address locations in a file mark table of the active storage system&#39;s volatile memory. When the selected disk drive receives a SPACE command to move to the next or previous number of file marks, the main board  102  retrieves the cache memory entry and moves the disk drive&#39;s LBA pointer to the file mark location. When the active system main board  102  receives a READ or WRITE command, it will check the file mark cache memory to insure that the request does not cross a file mark boundary of the selected drive. If it does not, it will read or write the requested data file. If it does, then the active system main board  102  will issue a CHECK_CONDITION response to the host system.  
      In another alternative embodiment, a data preservation system is realized which embodies desirable characteristics of a RAID array with file access times less than 100 milliseconds and random data access, and also embodies desirable characteristics of a tape library which include ability to passivate a data volume by removing it from the drive thereby reducing both exposure and management costs while maintaining a relatively low demand upon electrical and thermal resources (because of the small number of active devices). With conventional hard disk drive interconnect architectures it has been extremely difficult to provide a system which has the best characteristics of a random access RAID array and a tape library. Recent advances in storage networking offer new architectural alternatives. For example, if each hard disk drive of the array uses the TCP/IP internet protocol and employs an Ethernet-like physical transport technology, each hard disk drive may be provided with a unique address and can be readily disconnected and powered down, and then powered up and reconnected to the network without disturbing other storage devices or elements of the network. The native network interface may be provided at the drive level, or it may be provided at the magazine level, or the bay level. In the present example, the data protection system comprises a large number of high capacity (30 GByte to 100 GByte) hard disk drives, each drive having a direct network attachment and a unique network address.  
      A system controller controls the drives by providing power, monitoring status, and providing redundancy (e.g. data striping or mirroring) as well as virtualizing the interface between the drives and the (e.g. user data backup) application. The system network then effectively supports simultaneous transfer of data to and from a large number of rotating hard disk drives. While any one of the many known network connection arrangements are preferred, one particularly preferred example is several switched segments of Gigabyte Ethernet (GbE). In this approach, the computer support environment providing power and cooling is scaled to accommodate simultaneous operation of a small fraction, e.g. 5% to 10%, of the total array of disk drives simultaneously. The magazine approach described hereinabove can be employed to facilitate swapping of hard disk drives as well as removal and safe storage of hard disk drives containing archived user data.  
      Fundamental to the foregoing approach is the rotating hard disk drive unit itself. While any merchant market disk drive might be used, there are several characteristics that are highly desirable for disk drive units employed in the applications described herein. Among the most important disk drive characteristics are: a) a high confidence in data retention and integrity in an extended powered-off state; b) a native network interface; c) reliable, effective power cycling with minimum “drive ready” time latency from a powered-off condition; d) drive unit high data storage capacity and low cost per Gigabyte of user data stored; e) reliable initialization, control and monitoring for effective archive system management; and, f) convenient removal and replacement of disk drive units, and of magazines, to enable physical swap-out of drives, and removal and storage of drive magazines in an archive environment, most preferably of the type described hereinabove.  
      It will now be appreciated that the present invention provides protection of large user data files by employing disk drives in place of tape cartridges in a unique manner and configuration. The disk drives are most preferably arrayed within disk drive magazines. Each magazine holds a complement of high data capacity rotating hard disk drives which may emulate a like complement of tape cartridges. The disk drives may be initially employed in the active computing environment, and later on, after a nominal service life, the disk drives may be “retired” to provide the long-term data archival functions described herein. Alternatively, new hard disk drives may initially be employed to provide the tape emulation/data archive functions of the systems described herein.  
      Having thus described several embodiments of the present invention, it will now be appreciated that the objects of the invention have been fully achieved, and it will be understood by those skilled in the art that many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the spirit and scope of the invention. The disclosures and descriptions herein presented are purely illustrative and are not intended to be in any sense limiting.