Abstract:
Provided is a storage device and method for interfacing with an external device. The storage device includes a portable housing, a storage medium enclosed within the housing, and two data interfaces at different locations on the housing, wherein both the data interfaces are capable of providing data communication with the external device. A controller is enclosed within the housing and implements logic to select one of the two data interfaces to use to transfer data between the storage medium and the external device.

Description:
RELATED APPLICATIONS  
       [0001]    This application is related to the following commonly assigned and copending United States patent applications filed on the same date herewith and which are incorporated herein by reference in their entirety:  
         [0002]    “Gripper Assembly Apparatus for Interfacing with a Storage Device” by Daniel J. Winarski, Jesse L. Trall, Rodney J. Means, John E. Kulakowski, having attorney docket no. TUC920000088US2; and  
         [0003]    “An Automated Library System Including a Gripper Assembly Apparatus for Interfacing with a Storage Device” by Daniel J. Winarski, Jesse L. Trall, Rodney J. Means, John E. Kulakowski, having attorney docket no. TUC920000088US3. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0004]    1. Field of the Invention  
           [0005]    The present invention relates to a storage device apparatus having multiple interfaces.  
           [0006]    2. Description of the Related Art  
           [0007]    A tape library is comprised of multiple tape cartridges that may be separately accessed and handled by a robotic gripper assembly. The gripper assembly is capable of moving the tape cartridges between one or more racks of storage cells in which the cartridges are stored and a tape drive. If a user wants to access data on a tape cartridge in a cell, then the robotic gripper assembly must remove a tape cartridge from one tape drive, move the dismounted tape cartridge to one storage cell, move the gripper assembly to the storage cell to access the requested tape cartridge, and then transfer the cartridge to the tape drive for mounting and data access.  
           [0008]    Tape libraries allow for storage of substantial amounts of data at a low cost. However, dismounting a tape cartridge from one drive and mounting another tape cartridge from the rack of cells can take a substantial amount of time. Such delays in providing an application access to data in an unmounted tape cartridge can adversely affect the performance of the application.  
           [0009]    Due to concerns over the time required to mount tapes in a tape library, tape library developers continually strive to reduce cycle time. The cycle time indicates the time for the gripper assembly to dismount a tape from a current tape drive, return the tape cartridge to its assigned storage cell, access the requested tape cartridge from another cell, and then move and insert the accessed tape cartridge into one of the tape drives.  
           [0010]    For these reasons, there is a need in the art to provide improved technology for providing a library of storage devices.  
         SUMMARY OF THE PREFERRED EMBODIMENTS  
         [0011]    Provided is a storage device and method for interfacing with an external device. The storage device includes a portable housing, a storage medium enclosed within the housing, and two data interfaces at different locations on the housing, wherein both the data interfaces are capable of providing data communication with the external device. A controller is enclosed within the housing and implements logic to select one of the two data interfaces to use to transfer data between the storage medium and the external device.  
           [0012]    In further implementations, the storage device receives power from an external power supply. Two power interfaces at different locations on the housing are capable of receiving power from the external power supply to power the storage device.  
           [0013]    Further, detection is made of one data interface is engaged and capable of communicating with the external device. The I/O requests received from the external device are executed and data concerning the executed I/O requests is communicated through the detected data interface to the external device.  
           [0014]    The described implementations provide a hard disk drive structure having two sets of interfaces which may be engaged to provide data and power from either end. Such an arrangement is particularly useful for an automated tape library where different components can readily engage the storage device on either end. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    Referring now to the drawings in which like reference numbers represent corresponding parts throughout:  
         [0016]    [0016]FIGS. 1 a  and  1   b  illustrate a design of a hard disk drive in accordance with implementations of the invention;  
         [0017]    [0017]FIG. 2 illustrates a block diagram of the components in an automated library in accordance with implementations of the invention;  
         [0018]    [0018]FIG. 3 illustrates a design of a gripper assembly in accordance with implementations of the invention;  
         [0019]    [0019]FIG. 4 illustrates a layout of the storage cells and disk drives in an automated library in accordance with implementations of the invention;  
         [0020]    [0020]FIGS. 5 and 6 illustrate logic implemented in the library controller to transfer Input/Output (I/O) requests to the storage device in accordance with implementations of the invention; and  
         [0021]    [0021]FIGS. 7, 8, and  9  illustrate logic implemented in the storage device to use one of the two data interfaces to communicate data to the library controller in accordance with implementations of the invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]    In the following description, reference is made to the accompanying drawings which form a part hereof and which illustrate several embodiments of the present invention. It is understood that other embodiments may be utilized and structural and operational changes may be made without departing from the scope of the present invention.  
         [0023]    [0023]FIG. 1 a  illustrates a dual-end hard disk drive  2  in accordance with certain implementations of the invention. The disk drive components are maintained in a housing  4  and include a rotating disk  6  having at least one recording surface  8  for storing information, a motor (not shown) for rotating the disk, a voice coil motor  10 , an actuator arm  12 , actuator electronics  14 , and a transducer  16 . The transducer  16  is positioned in close proximity to the recording surface  8  to read and write data to the disk in a manner known in the art, e.g., through a magnetoresistive (MR) or giant magnetoresistive (GMR) read/write head or compound actuator head structure as known in the art. The arm electronics  14  provides carefully monitored power to the transducer  16  on the actuator  12 . The arm electronics  14  preamplifies the low level read signal from the transducers, e.g., MR and GMR transducers. The preamplified signal from the arm electronics  14  is sent to the data channel (not shown) for detection. The design and arrangement of components of disk drive systems are further described in “Magnetic Disk Drive Technology: Heads, Media, Channel, Interfaces, and Integration,” by Kanu G. Ashar (1997), which publication is incorporated herein by reference in its entirety.  
         [0024]    The dual-end disk drive  2  includes data interfaces  18 ,  20  on opposite sides of the disk drive  2 , which are both capable of receiving data from an external device, such as a computer bus. The data interfaces  18 ,  20  may utilize any data interface architecture and protocol known in the art, such as the Integrated Drive Electronics/AT Attachment Interface (IDE/ATA), the Small Computer System Interface (SCSI), Fibre Channel, etc.  
         [0025]    The interfaces  18  and  20  are connected to a common disk drive controller  22 , which manages the disk drive operations. The controller  22  uses memory  24 , which may comprise a volatile memory device, to buffer data to write to the recording surface  8  and data read from the recording surface  8  to return to an external system. The disk drive controller  22  manages the transfer of data from the memory  24  to the actuator arm  12  to write to the recording surface  8  in a manner known in the art. The disk drive controller  22  is capable of receiving data from both data interfaces  18 , 20 .  
         [0026]    The dual-end disk drive  2  further includes power interfaces  26 ,  28  on both ends of the disk drive. The power interfaces  26 ,  28  supply power to the power supply  30  which regulates the voltage suppled to the disk drive controller  22 , voice coil motor  10 , actuator arm  12 , and all other components in the dual-end disk drive  2 . The power supply  30  may also act as a power buffer to continue supplying power to the disk drive  2  when the power source is being switched from power interface  26 ,  28 . In certain implementations, the power connections are make-before-break, which means that the power connection at one interface  26  or  28  is made before power is broken at the other interface  26  or  28 . Power supply  30  is sufficiently robust to accommodate power from both interfaces  26 ,  28  and still modulate that power to the needs of hard disk drive  4 . Additionally, power supply  30  could include a rechargeable battery to function as a power buffer for hard disk drive  4  in case the power connections are break-before-make.  
         [0027]    The dual-end disk drive  2  implementation of FIG. 1 a  is capable of receiving power from interfaces  26  and  28 , as well as data from interfaces  18  and  20 . Further, the dual-end disk drive  2  includes indentations  32   a, b, c, d  on the side of the housing  4  to improve the capability of a gripper assembly, discussed below, to access and move the disk drives.  
         [0028]    [0028]FIG. 1 b  further shows an implementation of the memory  24  in the disk drive  2 . A read buffer  34  stores data retrieved from the recording surface  8  to return to a requesting application. A write buffer  36  stores data received from the external application to write to the recording surface  8 . I/O queue  38  queues I/O requests in a manner known in the art, e.g., First-In-First-Out (FIFO). An interface indicator  40  indicates the set of data and power interfaces at one end  18 ,  26  and/or  20  and  28  that are engaged. The interface indicator  40  may indicate one end of data and power interfaces or both ends if both ends are engaged. If the dual end disk drive is engaged on both ends, then the interface indicator  40  may indicate one end as the primary interface to use and the other end as a secondary interface that is engaged but not used for I/O. An external device address  42  indicates the address of the device to which the disk drive controller  22  communicates data and other status information. This address may comprise the address of the gripper assembly and drive interface  62  or the address of a drive interface on the library backplane  60  shown in FIG. 2 and discussed below. The external device address  42  may comprise a primary and secondary address if both ends are engaged, where the primary address indicates the address currently used for data communication.  
         [0029]    In certain implementations, data may be stored on only one or both surfaces of the disk  8 . In such case, there would be multiple suspensions connected to the arm with transducer heads to read and write on both surfaces of the disk. Moreover, as known in the art, the disk drive may include a stack or platters of disks that are mounted in parallel on a spindle for simultaneous rotation. In such case, there would be multiple heads, one for each recording surface of each disk in the stack. In these multi-platter systems, a cylinder is formed of the combination of concentric rings on multiple disks along the same vertical axis.  
         [0030]    [0030]FIG. 2 illustrates components within an automated library  50  in which the dual-end hard disk drives described with respect to FIG. 1 a  are used. The automated library  50  includes a library controller  52 , a memory  54 , accessible to the library controller  52 , a storage array  56  of storage cells for holding hard disk drives  58 , including the dual-end hard disk drive  58  (shown as dual-end disk drive  2  in FIG. 1 a , input/output slots (not shown) through which the user may insert the dual-end hard disk drives  58 , and one or more disk drive interfaces on the library backplane  60  in which the data interface  18 ,  20  of the dual-end disk drives  60  may be connected to allow for the transfer of data. In certain implementations, the dual-end disk drives  58  can be “hot plugged” in and out of the drive interfaces on the library backplane  60  and gripper assembly  62 . The disk drive interfaces on the library backplane  60  are on a backplane of the automated library  50 . A gripper assembly and drive interface  62  provides a gripper and other movement electronics to transfer the disk drives  58  between the storage array  56  and drive interfaces on the library backplane  60 .  
         [0031]    The library controller  52  is preferably implemented as a microprocessor and includes interfaces and code to control and manage the operation of the components in the automated library  50 , including the gripper assembly and driver interface  62  and drive interfaces on the library backplane  60 . The library controller  52  operates under control of microcode  61 , which is embedded in a non-volatile storage unit, e.g., hard disk drive, PROM, EEPROM, non-volatile RAM, etc. The library controller  52  utilizes the memory  54  to store various information, such as a dual-end disk drive map  64  maintaining information on where each hard disk drive  58  is located, i.e., in the storage array cell  56 , in the gripper assembly and drive interface  62  en route from a storage cell array to the drive interface on the library backplane  60 . If the library element includes a disk drive, then the disk drive map  64  would include information on the contents of the disk drive maintained in the library element, such as volume information. The library  50  further includes servo electronics  66  that provides the interface between the library controller  52  and other electromechanical components to convert digital control signals from the library controller  52  to signals capable of controlling electro-mechanical components.  
         [0032]    A library operator may directly control operations and the management of the dual-end disk drives  2  through an operator terminal  70 , consisting of a display device and keyboard, to interface with the library controller  52 . A host system  72  may send commands to the library controller  52  to control operations within the automated library  50  or perform read or write operations on volumes within cartridges managed by the library controller  52 . The host system  72  and library  50  may communicate via SCSI adaptors and a SCSI cable. In further embodiments, the host system  72  and library  50  may communicate via any communication means known in the art, e.g., LAN, WAN, Storage Area Network (SAN), Fibre Channel, etc.  
         [0033]    [0033]FIG. 3 illustrates one implementation of the gripper assembly and drive interface  62 . The gripper assembly and drive interface  62  engages the dual-end disk drive  2  shown in FIG. 1 a  and any other drives  58  in the system, such as hard disk drives known in the art. The gripper assembly  62  includes a gripper pair  102 ,  104 . Extendable protrusions  106  and  108  on the gripper pair  102  and  104 , respectively, are intended to mate with a pair of indentations  32   a, b, c, d  (FIG. 1 a ) on the disk drive  2  to provide a solid engagement or grip of the dual-end disk drive housing  4 . To release the disk drive  2 , the gripper assembly  62  could release or retract the protrusions  106  and  108  to disengage from the indentations  32   a, b, c, d . The gripper  62  further includes a backplane  110  including a data interface  112  and power interface  114  that is capable of mating with the data interfaces  18 ,  20  and power interfaces  26 ,  28  on both sides of the dual-end disk drive  2  to allow for the transfer of data and power from the gripper backplane  110  to the dual-end disk drive  2 . The gripper assembly  62  may include a power supply to supply power to the storage device through the power interfaces, or receive power from a power supply source external to the gripper assembly  62 .  
         [0034]    The gripper  62  further includes a mounting bracket  116  that engages a vertical shaft  118 . The library controller  52  can control the gripper assembly  62  to move in the vertical direction along the shaft  118 . The gripper assembly  62  may further include servo-electronics to allow for movement in the horizontal plane to insert or remove a hard disk drive into a storage cell, e.g., storage bin, or the drive interfaces on the library backplane  60 .  
         [0035]    [0035]FIG. 4 provides one possible arrangement of an automated library of dual end disk drives. The storage array  56 , drive interfaces on the library backplane  60 , and gripper assembly and drive interface  62  in the automated library  50  of FIG. 3 are shown as storage array  156 , drive interfaces  160   a, b, c, d , and gripper assembly  162  in automated library  150  in FIG. 4. In FIG. 4, the storage array  156  is comprised of two columns  172   a, b  of storage cells. The storage cells are shown as slots in the columns  172   a, b  that are capable of holding hard disk drives, such as the dual end disk drive  2  of FIG. 1. For example, storage cells  174   a, b , and  c  include hard disk drives  158   a, b, c  and storage cells  174   d, e  are empty. The drive interfaces on the library backplane  160   a, b, c, d , referenced as  60  in FIG. 2, include power and data interfaces (not shown) to mate with power  26 ,  28  and data  18 ,  20  interfaces on the dual end disk drives  2  (FIG. 1), or the power and data interfaces of hard disk drives known in the art. The gripper assembly and drive interface  162 , shown as  62  in FIGS. 2 and 3, can move vertically along vertical shaft  180  and horizontally along horizontal shafts  182   a, b . Those skilled in the art will appreciate that there are numerous ways to implement the layout of an automated library, including storage cells and drives at different locations. For instance, in certain implementations, the gripper assembly and drive interface  162  may have to move along a track on the floor to access different storage arrays and different drive interfaces on the library backplane. Although FIG. 4 illustrates two columns of storage cells (bins), in additional implementations, the storage array may include several columns of storage cells. In such case, the gripper assembly  162  would include the capability to traverse in the horizontal and vertical directions to access any storage cell in the storage array  56 .  
         [0036]    [0036]FIGS. 5 and 6 illustrate logic implemented in the library controller  52  (FIG. 2) to manage a library of dual-end hard disk drives  2  (FIG. 1 a ) and I/O requests directed to the hard disk drives. Control begins at block  200  with the library controller  52  receiving an I/O request with respect to a volume in one dual-end hard disk drive (HDD) in the automated library. The library controller  52  determines (at block  202 ) the current location of a target hard disk drive  158   a, b, c  (FIG. 4) including data subject to the I/O request. With reference to FIGS. 1 a ,  2  and  4 , the target hard disk drive may be at one of three locations in the library  50 , within a storage cell  174   a, b, c, d, e  in the storage array  56 ,  156 ; held in the gripper assembly and drive interface  62 ,  162 ; or engaged with a drive interface on the library backplane  60 ,  160   a, b, c, d . If (at block  204 ) the target hard disk drive (HDD) is in a disk drive interface on the library backplane  60 ,  160   a, b, c, d  then the library controller  52  builds (at block  206 ) an I/O request to the device address of the drive interface on the library backplane  60 ,  160   a, b, c, d  engaged with the target hard disk drive. Control then proceeds (at block  207 ) to block  250  in FIG. 6 to send the I/O request to the drive interface. Otherwise, if (at block  208 ) the target hard disk drive (HDD) is engaged in the gripper assembly  62 ,  162  (FIG. 3), then the library controller  52  proceeds to block  220  to estimate the workload time of the job to determine whether to transfer the tape to a drive interface on the library backplane  160 ,  160   a, b, c, d.    
         [0037]    If (at block  208 ) the target hard disk drive is not engaged with the drive interface of the gripper assembly  62 ,  162  or library backplane  160 ,  160   a, b, c, d , then the target hard disk drive (HDD) must be located in a storage cell, e.g., storage cell  174   a, b, c, d, e  (FIG. 4) in the storage array  56 ,  156 . In such case, the library controller  52  sends (at block  212 ) a command to the gripper assembly  62 ,  162  to engage and grip the target hard disk drive (HDD) in its cell in the storage array  56 ,  156 . Upon receiving (at block  214 ) a message or signal from the gripper assembly  62 ,  162  indicating that the target hard disk drive (HDD) is engaged with the interfaces on the gripper assembly  62 ,  162 , the the library controller  52  performs two different branches of action. The first branch involves supplying power (at block  216 ) to the power interface  114  (FIG. 3) on the gripper assembly  62 ,  162  and building (at block  218 ) the I/O request to send to the gripper assembly  62 ,  162 . Control then proceeds (at block  207 ) to block  250  in FIG. 6 to send the built I/O request to the gripper assembly drive interface  62 ,  162 .  
         [0038]    The second branch from block  214  involves the library controller  52  determining whether to move the target hard disk drive to a drive interface on the library backplane  60 ,  160   a, b, c, d  or to complete the I/O request through the gripper assembly drive interface  62 ,  162  without moving the target disk drive to the drive interface on the library backplane  60 ,  160   a, b, c, d . To make this determination, the library controller  52  estimates (at block  220 ) the workload time of the I/O request. The estimated workload time may be determined by an equation that calculates workload as a function of the number of blocks involved in the I/O request and the type of I/O request, i.e., read/write. The library controller  52  then determines (at block  222 ) whether the estimated workload time plus the estimated disk spin-up or initialization time, i.e., the time to initialize the target disk for I/O operations, which may be a predetermined fixed number, is greater than the estimated travel time from the storage cell including the target hard disk drive to the drive interface on the library backplane  60 ,  160   a, b, c, d . For the estimated travel time, the library controller  52  may use a predetermined average travel time based on historical data, or calculate the estimated travel time based on the distance to travel from the specific storage cell  174   a, b, c, d, e  to the drive interface on the library backplane  160   a, b, c, d.    
         [0039]    If (at block  222 ) the estimated workload time and disk spin-up initialization exceeds the travel time, then it would be advantageous to transfer the target hard disk drive to the drive interface on the library backplane  60 ,  160   a, b, c, d . The I/O operation can be initiated while the target hard disk drive is in the gripper assembly and the remainder of the I/O operation can be performed at the drive interface on the library backplane  60 ,  160   a, b, c, d . This will free-up the gripper assembly  62 ,  162  to service additional I/O requests at other hard disk drives in the storage array  56 ,  156 . In such case, the library controller  52  further determines (at block  224 ) if the current library utilization is less than a light utilization threshold value indicating a low utilization. If the current library utilization is relatively low, then the I/O request can be serviced entirely through the gripper assembly data interface  62 ,  162  without affecting system performance because it is unlikely that the gripper assembly  62 ,  162  will be needed for another I/O request before the current I/O operation completes.  
         [0040]    The library utilization indicates the percentage of time the gripper assembly  62 ,  162  is occupied engaging hard disk drives. The utilization can be determined by dividing the hard disk drive mount requests performed over a past time period, e.g., hour, by the maximum number of mount requests that can be performed in an hour. The time to perform a mount includes the time to remove a hard disk drive from one of the drive interfaces on the library backplane  60 ,  160   a, b, c, d , return the removed drive to its storage cell, access the target hard disk drive from another storage cell and then move the accessed hard disk drive to the disk drive interface on the library backplane  60 ,  160   a, b, c, d . For instance, if the gripper assembly  60 ,  162  takes ten seconds to mount a hard disk drive (HDD) from a storage cell, then the maximum mounts per hour is 360. The actual number of mounts per hour is then divided by this maximum amount, e.g., 360, to obtain the gripper assembly  62 ,  162  utilization. Further, the gripper assembly  62 ,  162  response time or time to service is set forth in equation (1) below, where the variable U is the gripper assembly  62 ,  162  utilization and “Service Time” is some average time for the gripper assembly  62 ,  162  to complete a mount request.  
               Response                 Time     =       1     (     1   -   U     )       *   ServiceTime             (   1   )                               
 
         [0041]    With equation (1) above, the more the gripper assembly  62 ,  162  is utilized, the longer the queue time that increases the base service time. For example, when utilization (U) is zero, the response time equals the service time. However, as the utilization (U) approaches unity, the response time goes to infinity.  
         [0042]    If (at block  224 ) the library utilization is greater than the low utilization threshold, i.e., the library is highly utilized, then the library controller  52  sends (at block  226 ) the command to move the gripper  62 ,  162  engaging the target hard disk drive (HDD) to one drive interface on the library backplane  60 ,  160   a, b, c, d . In this way, while the gripper assembly  62 ,  162  is en route to the disk drive interface  60 ,  160   a, b, c, d , the disk drive can be initialized and data can be transferred to partially or fully complete I/O requests, thereby minimizing any delays in processing I/Os. If the conditions at blocks  222  and  224  are not satisfied, then the target hard disk drive is not moved to a drive interface on the library backplane  60 ,  160   a, b, c, d.    
         [0043]    After the library controller  52  builds the I/O request at block  206  or  218  to a drive interface at the gripper assembly  62 ,  162  or library backplane  60 ,  160   a, b, c, d , control proceeds (at block  207 ) to block  250  in FIG. 6 transmit (at block  250 ) the I/O request to the hard disk drive. With respect to FIG. 6, at block  252 , the library controller  52  marks (at block  252 ) the disk drive as inactive in the disk drive map  64  and transmits a command to open (at block  254 ) the directory on the disk drive. The library controller  52  then transmits (at block  256 ) the built I/O request to the drive interface including the hard disk drive. After completing all I/O requests against the hard disk drive, the library controller  52  updates (at block  258 ) and closes the directory on the target hard disk drive and marks (at block  260 ) the hard disk drive as inactive in the disk drive map  64 . Control then proceeds to block  200  in FIG. 5 to process further received I/O requests.  
         [0044]    [0044]FIGS. 7, 8, and  9  illustrate logic implemented in the disk drive controller  22  of the dual-end disk drive  2  of FIG. 1 a  to execute I/O requests. With respect to FIG. 7, upon the disk drive controller  22  detecting (at block  300 ) engagement or disengagement with one set of data  18 , 20  and power  26 ,  28  interfaces on one end of the housing  4 , the disk drive controller  22  sets (at block  302 ) the interface indicator  40  to the set of data  18 ,  20  and power  26 ,  28  interfaces that are currently engaged, which can indicate no sets engaged, one set engaged or both sets on both ends engaged. This information enables the disk drive controller  22  to determine which interfaces are available for data and power communication. At block  304 , the disk drive controller  2  sets the external device address  304  to the address of the external device(s) engaged through the interfaces  18 ,  20 , i.e., the address of the drive interface on the gripper assembly  62  and/or library backplane  60 . From block  302 , control returns to block  300  to detect any further engagements or disengagements with interfaces.  
         [0045]    [0045]FIGS. 8 and 9 illustrate logic the disk drive controller  22  executes to process I/O requests in the I/O queue  38 . Control begins at block  350  with the disk drive controller  22  accessing a pending I/O request in the I/O queue  38 . If (at block  352 ) the interface indicator  40  indicates engagement with only one of data  18 , 20  and power  26 ,  28  interfaces, then the disk drive controller  22  executes the I/O request against the recording surface  8 , i.e., performs the requested read or write operation, and then returns data or status through the interface identified in the interface indicator  40  to the external device address  42 . If the I/O request is a read and the requested data is in the read buffer  34 , then the disk drive controller  22  can return the requested data from the read buffer  34  without having to read the requested data from the recording surface  8 .  
         [0046]    If (at block  352 ) the interface indicator  40  indicates engagement with the data  18 ,  20  and power  26 ,  28  interfaces on both ends, i.e., both primary and secondary set of interfaces, then the disk drive controller  22  proceeds (at block  358 ) to block  400  in FIG. 9 if (at block  356 ) the I/O request is a write. If the I/O request is a read (at block  356 ) and the requested data is in the read buffer  34  (at block  360 ), then the disk drive controller  22  returns (at block  362 ) the requested data from the read buffer  34  through the primary data  18 ,  20  interface indicated in the interface indicator  40  to the external device address  42 . If the requested data is not in the read buffer  34 , then the disk drive controller  22  instructs (at block  364 ) the actuator assembly  10  and arm  12  to read the requested data from the recording surface  8 . The data retrieved from the recording surface  8  is stored (at block  366 ) in the read buffer  34 .  
         [0047]    In certain implementations, the disk drive controller  22  maintains a trigger pointer to a location in the read buffer  34  to use as an indicator of when to switch from using the data  18  and power  26  interfaces one end to using the interfaces on the other end, i.e., using the data  20  and power  28  interfaces. Such a switch would involve switching from using the data  112  and power  114  interfaces on the gripper assembly  62  (FIG. 3) to using the drive interfaces on the library backplane  60 ,  160   a, b, c, d . In certain implementations, the trigger pointer would point to the end of a sector boundary, so that the transition to another data interface  18 ,  20  occurs at the end of one sector boundary and before the beginning of the next sector. Transitioning to the other data interface  18 ,  20  at the end of a sector boundary does not interfere with the transmission or receipt of any error correction or longitudinal redundancy codes, which are typically located at the end of a sector boundary to provide error correction for the data in the sector. Additionally, the size of the buffer  34 ,  36  may determine when to transition from using one data interface  18 ,  20  to the other. For instance, if the file involved in the read/write operation is larger than the buffer  34 , 36  used, then the disk drive controller  22  would switch data interfaces  18 ,  20  on the sector boundary. However, if the file(s) are smaller than the buffer  34 ,  36 , then the controller  22  may switch data interfaces  18 , 20  at the conclusion of one file, and before beginning the read/write with respect to another file.  
         [0048]    If (at block  368 ) the controller  22  stores data to the read buffer  34  location addressed by the trigger pointer after detecting that the data  18 ,  20  and power  26 ,  28  interfaces are engaged on both ends, then the controller  22  signals (at block  370 ) the library controller  52  to use the disk drive interfaces on the library backplane  60 ,  160   a, b, c, d  instead of the gripper assembly drive interface  62 ,  162 . To use the interfaces on the other end, the controller  22  would set (at block  372 ) the interface indicator  40  to only the interfaces engaged with the drive interface on the library backplane  60 ,  160   a, b, c, d  and set the external device address  42  to the address of the drive interface on the library backplane  60 ,  160   a, b, c, d , i.e., the secondary interface and address in the interface indicator  40  and external device address  42  become the primary. Upon receiving this message, the library controller  52  would then set a flag or other indicator to address the disk drive data interface  58  to send data to the subject hard disk drive. The disk drive controller  22  then disengages (at block  374 ) from using the primary end, which is the end engaged with the gripper assembly and drive interface  62 ,  162 . The disk drive controller  22  would then return (at block  362 ) the requested data to the disk drive interface on the library backplane  60 ,  160   a, b, c, d  and use the library backplane for subsequent I/O requests. If (at block  368 ) the retrieved data is not stored at the trigger pointer location, then the controller  22  returns (at block  362 ) the requested data through the gripper data interface  112  (FIG. 3) to the library controller  52  (FIG. 2).  
         [0049]    If (at block  356 ) the I/O request was a write, then the disk drive controller  22  determines (at block  400  in FIG. 9) whether the write buffer  36  is filled beyond a threshold level. If so, then the disk drive controller  22  performs (at block  402 ) blocks  370 ,  372 , and  374  to switch and signal the library controller  52  to switch to using the engaged drive interface on the library backplane  60 ,  160   a, b, c, d . The disk drive controller  22  then writes (at block  404 ) the data in the write buffer  36  to the recording surface  8  (FIG. 1 a ) and returns status through the primary interface identified in the interface indicator  40  to the primary device address indicated in the external device address  42 . Control then proceeds (at block  406 ) to block  350  in FIG. 8 to process the next I/O request. If (at block  400 ) the write buffer  36  is not filled beyond the threshold, then control proceeds to block  404  to process the write request. Signaling the library controller  52  after the write buffer  36  fills to a threshold level minimizes down time because even if the library controller  52  experiences delays in streaming write requests upon receiving the message to switch to using the drive interface  58  address, such delays at the library controller  52  end will not affect performance because the disk drive controller  22  can continue to access and process pending write requests in the write buffer  36 . The threshold level is set sufficiently high so that the write buffer  36  continues to supply write requests for the controller  22  to process during any delay the library controller  52  experiences in submitting write requests when switching to the drive interface on the library backplane  60 ,  162 ,  a, b, c, d  to access the hard disk drive.  
         [0050]    In implementations where the gripper assembly includes a drive interface, the dual end disk drive would be engaged with the gripper assembly and drive interface  62 ,  162  upon the first detected engagement. The second detected engagement would be with the drive interface on the library backplane  60 ,  160   a, b, c, d . In such implementations, the logic may take this sequence of events into account to prevent any switching over to another interface after the first switch and disengagement once the disk drive is engaged with the drive interface on the library backplane  60 ,  160   a, b, c, d  where the dual end disk drive will remain until I/O completes and the disk drive is removed and returned back to a storage cell. In alternative implementations the assumptions in the logic may differ depending on the architecture of the library.  
         [0051]    The described implementations provide a design for the disk drives and the gripper assembly that minimizes time to access the hard disk drive, even as the hard disk drives are transferred from the storage array  56 ,  152   a, b  to the drive interfaces  60 ,  160   a, b, c, d  as the hard disk drive can be accessed through the gripper assembly  62 ,  162 . This dual-end hard disk drive design further minimizes any delays in accessing the disk because the gripper  62 ,  162  (FIGS. 2, 3,  4 ) does not need to turn the disk drive around in order to mount the disk drive onto the drive interface on the library backplane  62 ,  162   a, b, c, d . Still further, because the disk drives are dual-end, they can be swapped between pickers without the need to rotate the hard disk drive or interrupt the I/O flow. For instance, when swapping a dual-end hard disk drive between pickers, both pickers can be engaged with the data interfaces at opposite of the hard disk drive. This allows pickers to swap a hard disk drive and time the disengagement of one picker to minimize any interruption to data flow. Pickers on the same track may also swap hard disk drives to avoid collisions. Still further, the dual-end hard disk drives would not have to be rotated in either an Input/Output station or a pass-through station between library modules because they may be engaged from either end.  
       Additional Implementation Details  
       [0052]    The preferred embodiments may be implemented as a method, apparatus or article of manufacture using standard programming and/or engineering techniques to produce software, firmware, hardware, or any combination thereof. The term “article of manufacture” as used herein refers to code or logic implemented in hardware logic (e.g., an integrated circuit chip, Field Programmable Gate Array (FPGA), Application Specific Integrated Circuit (ASIC), etc.) or a computer readable medium (e.g., magnetic storage medium (e.g., hard disk drives, floppy disks, tape, etc.), optical storage (CD-ROMs, optical disks, etc.), volatile and non-volatile memory devices (e.g., EEPROMs, ROMs, PROMs, RAMs, DRAMs, SRAMs, firmware, programmable logic, etc.). Code in the computer readable medium is accessed and executed by a processor. The code in which preferred embodiments are implemented may further be accessible through a transmission media or from a file server over a network. In such cases, the article of manufacture in which the code is implemented may comprise a transmission media, such as a network transmission line, wireless transmission media, signals propagating through space, radio waves, infrared signals, etc. Of course, those skilled in the art will recognize that many modifications may be made to this configuration without departing from the scope of the present invention, and that the article of manufacture may comprise any information bearing medium known in the art.  
         [0053]    In the described implementations, the gripper assembly  62  moves the disk drive to the drive interface  60  ( 160   a, b, c, d ). However, in an alternative implementation, the library may employ one or more grippers  62  to move between the dual-end hard disk drives and engage the disk drive to provide access without ever moving the hard disk drive to a driver interface.  
         [0054]    [0054]FIG. 4 illustrated one possible implementation of the automated library, including columns of storage arrays with the disk drive interfaces  58  directly in the column in the cells. In additional implementations, the library may comprise a large enclosure and the gripper assembly may be capable of moving along a track to different storage arrays and bays of drive interfaces.  
         [0055]    In the described implementations, the storage device comprised a dual-end hard disk drive. In alternative implementations, the storage device may comprise any storage device known in the art maintained in a housing that provides non-volatile storage of data that can be accessed from different locations or ends on the housing including the storage medium. In the described implementations, the storage medium comprised a magnetic disk surface. In alternative implementations, the storage medium may comprise other storage mediums known in the art, such as an electronic storage device, etc.  
         [0056]    In the described implementations, the two sets of interfaces were placed on opposite ends of the housing. Additionally, the duplicate data and power interfaces may be placed on any two planes of the housing. Additionally, there may be more than two sets of interfaces on the housing to provide for still additional degrees of access to the storage device.  
         [0057]    The logic implementation of FIGS.  5 - 9  describe specific operations occurring in a particular order. In alternative embodiments, certain of the logic operations may be performed in a different order, modified or removed and still implement preferred embodiments of the present invention. Morever, steps may be added to the above described logic and still conform to the preferred embodiments.  
         [0058]    The foregoing description of the preferred embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto. The above specification, examples and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.