Patent Publication Number: US-8127068-B2

Title: Removable cartridge storage devices and methods

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/586,085, entitled “Removable Cartridge Disk Device and Methods”, filed Jul. 6, 2004, which is incorporated herein by reference. 
     This application is also related to U.S. patent application Ser. No. 11/122,322, entitled “Data Replication Systems and Methods”, filed on May 3, 2005, U.S. Provisional Application No. 60/586,087 entitled “Electronic Storage Cartridge”, filed on Jul. 6, 2004 and U.S. Provisional Application No. 60/586,086, entitled “Auto-Replicating System for Removable Data Cartridges”, filed on Jul. 6, 2004. The details of these applications are hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention generally relates to data storage devices. More specifically, the present invention relates to removable cartridge storage devices. 
     Computer backup has traditionally been performed using tape drive technologies. Tape drive technologies have been popular in the use of backup systems for a variety of reasons. One reason is that tape media has generally had the lowest cost per bit of storage. Additionally, tape devices use removable tape cartridges, which may be taken to an off-site location to provide for disaster recovery. A third reason tape devices are popular is because of the long-term archive characteristics of tape media. 
     As the storage capacity in stand-alone and networked computers has increased, so have the demands on backup systems. One of the current trends is the use of mechanical automation systems, such as tape cartridge autoloaders and robotic tape libraries, to expand the capacity of the backup system. The cartridge autoloaders and tape libraries hold multiple removable tape cartridges. One or more tape drives is embedded inside a storage area containing one or more magazines of tape cartridges. These systems also include a mechanical system to automate the cartridge changing operation. The mechanical system is used to load and unload the cartridges between the magazines and the tape drives. 
     A prior art standalone tape drive that may be used to perform data backups is illustrated in  FIG. 1 . The tape drive  100  includes a system controller  102 . The system controller  102  includes an interface to a host computer  120 . By way of example, the interface to the host computer may be Small Computer Systems Interface (SCSI), Fiber Channel (FC), or other type of communication interface. The system controller  102  also includes a microprocessor which performs data formatting for the tape medium. The tape drive  100  also includes a tape recording mechanism  104  which magnetically encodes the formatted data on magnetic tape cartridges  106 ,  108 ,  110 . Tape recording mechanism  104  is also used to read data from the magnetic tape cartridges  106 ,  108 ,  110 . Oftentimes, the backup of host computer may require more storage capacity than that available on a single tape cartridge  106 ,  108 ,  110 . Thus, if the tape drive is not part of a tape autoloader system, an operator may be required to manually remove a tape cartridge  106  which has reached its data storage capacity, and insert a new tape cartridge  108 , so that the transfer of data from host computer to magnetic tape cartridges may continue. The operator may be required to repeat this process multiple times before the backup is completed. 
       FIG. 2  illustrates a second prior art system that has multiple tape drives  210 ,  220  coupled to a host computer system  200 . Both tape drives  210 ,  220  include system controllers  212 ,  222 . Each of the system controllers  212 ,  222  has an interface to host computer system  200 , such as a SCSI or FC interface. The tape drives  210 ,  220  additionally includes a tape recording mechanism  214 ,  224 , which may be used to magnetically encode data on a magnetic tape cartridge  216 ,  226 . 
     In some embodiments, a tape automation system, such as the tape autoloader  300  illustrated in  FIG. 3  may be used to automate cartridge changing operations. The tape autoloader includes at least one tape drive  320 . Multiple storage slots  311 - 317  may be used to house tape cartridges  301 - 307 . In some embodiments, the storage slots  311 - 317  may be part of a removable magazine to facilitate the loading and unloading of cartridges. 
     A motorized mechanism  330  may be used to move the tape cartridges  301 - 307  to and from the tape drive  320 . The motorized mechanism may also optionally be used to move cartridges to and from an access opening (not shown) to the tape autoloader  300 , which may be used to enter and remove tape cartridges  301 - 307  into the tape autoloader  300 . In one embodiment, the motorized mechanism  300  may include a cartridge picker arm  334  and a picker motor  332  to operate the cartridge picker arm  334 . A drive motor  336  is used to drive the motorized mechanism  330 . 
     The tape autoloader  300  has at least two interfaces  352 ,  354  to host computer  350 . By way of example, interfaces  352 ,  354  may be SCSI or FC interfaces. One interface  354  is provided for each tape drive  320  included in the tape autoloader. This interface  354  may be referred to as the “data path” interface and is used to send data and tape drive commands to a system controller component of tape drive  320 . In embodiments in which the tape autoloader  300  includes multiple tape drives, the data path interfaces to each tape drive may be coupled to different host computers. A second interface  352  (also called the “control path”) is used to send media changer commands to the autoloader mechanism controller  340 , such as load, unload, and audit commands. The autoloader mechanism controller  340  includes electronics and software used to actuate the motorized mechanism  330  for movement of tape cartridges  301 - 307  and auditing of the tape autoloader  300 . In some embodiments, the control path interface  352  may be coupled to a second host computer. The autoloader mechanism controller  340  may also be communicatively coupled to tape drive  320  for communications between these components. Although multiple tape drives in the tape autoloader  300  may be operated in parallel, the mechanical system  330  used to load and unload cartridges can only move a single cartridge at a time. Additionally, each tape drive  320  has its own system controller which requires a separate “data path” interface to a host computer  350 . 
     Another prior art system that may be used to perform backups is illustrated in  FIG. 4 .  FIG. 4  illustrates a virtual tape system  400 . The virtual tape system  400  uses a HDD or array of HDDs  404  for storage of data. A system controller  402  may provide emulation of tape interface commands to enable the virtual tape system to interface to a backup software application using a native tape command set. Thus, the system controller  402  may communicate with a host computer  410  over an interface using SCSI or FC tape commands. The system controller  402  also formats received data to a disk format for recordation on HDDs  404 . The HDDs may be in a RAID or JBOD configuration and may be logically partitioned to create the illusion of multiple discrete data cartridges to which the data is recorded. However, in this type of system, the virtual data cartridges are not physically separable from one another since they are all contained in a single disk or disk array. Thus, the data cannot be removed to an offsite location for disaster recovery protection. 
     BRIEF SUMMARY OF THE INVENTION 
     Removable cartridge storage devices and methods are disclosed. In some embodiments, the removable cartridge storage device comprises a plurality of cartridge holders, a system controller, and a switching component. The cartridge holders each include an electrical connector configured to removably couple with a mating electrical connector of a portable data cartridge having an electronic interface (e.g., data cartridges having embedded hard disk drives or flash memory). In some aspects, the cartridge holders may each define an opening exterior to the removable cartridge storage device to receive portable data cartridges. The system controller be configured to process commands transmitted to the removable cartridge storage device. The switching component may be coupled between the cartridge holders and the system controller, and may be used to electronically switch connections between the system controller and each of the cartridge holders. Thus, the system controller may electrically switch data operations to different data cartridges. Optionally, in some embodiments, the removable cartridge storage device may also comprise a serial advanced technology attachment (SATA) interface, coupled between the system controller and the cartridge holders. 
     The system controller may include an interface (e.g., SCSI, Fiber Channel interface, etc.) to receive data commands. In some aspects, the interface may also be used to receive media changer commands (e.g., SCSI media changer commands) or a second interface may be included in system controller to receive media changer commands. Thus, the system controller may be configured to execute the media changer commands. Merely by way of example, media changer commands processed by the system controller may include move medium commands (e.g., SCSI Move Medium, SCSI Exchange Medium), audit commands (e.g., SCSI Initialize Element Status, SCSI Read Element Status), system configuration commands, system diagnostic commands, or other types of media changer commands. 
     In some instances, the system controller may emulate an automated tape device or other tape device. System controller may thus be configured to receive and execute sequential tape device commands and/or automated tape device commands autoloader system. Thus, the system controller may translate received commands from tape commands to the appropriate command for the autoloader device using data cartridges with electronic interfaces. 
     The system controller may, in some aspects, operate portable data cartridges removably coupled with the cartridge holders independently of the other portable data cartridges. In some aspects, the system controller may be configured to write data to the portable data cartridges sequentially. In other aspects, system controller may be configured to perform copy operations without transferring data to a host computer. 
     In other embodiments, the removable cartridge storage device comprises a cartridge holder, a system controller, and a cartridge interface communicatively coupled between the system controller and the cartridge holder. The cartridge holder has an electrical connector configured to removably couple with a mating electrical connector of a portable data cartridge having an electronic interface. The system controller is configured to emulate a tape device and to process commands transmitted to the removable cartridge storage device. The cartridge interface provides electronic signaling to a portable data cartridge removably coupled with the cartridge holder. 
     In other embodiments, a method is disclosed which comprises receiving, at a storage device, a data command (e.g., read, write, copy) from a host computer system. The data command is associated with a first portable data cartridge having an electronic interface. The first portable data cartridge is removably coupled with the storage device. Communications are electronically switched from a second portable data cartridge removably coupled with the storage device to the first portable data cartridge and the data command is executed. 
     In some aspects, the data command may be a tape command. In other aspects, the data command may comprise a copy command. The copy command may be executed by reading data from the first portable data cartridge and electronically switching to a target portable data cartridge removably coupled with the storage device. The data may be written to the target portable data cartridge without transferring the data to the host computer system. 
     Further aspects of the method may comprise receiving a move media command and executing the move media command electronically. Alternatively, or additionally, the method may comprise receiving an audit command and auditing the storage device electronically. 
     A further understanding of the nature and advantages of the present invention may be realized by reference to the remaining portions of the specification and the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Illustrative embodiments in accordance with the invention are illustrated in the drawings in which: 
         FIG. 1  illustrates a prior art tape drive; 
         FIG. 2  illustrates a prior art multiple tape drive system; 
         FIG. 3  illustrates a prior art tape autoloader; 
         FIG. 4  illustrates a prior art virtual tape system; 
         FIG. 5A  illustrates an exemplary embodiment of a removable cartridge storage device; 
         FIG. 5B  illustrates an exemplary embodiment of the cartridge holder in  FIG. 5A ; 
         FIG. 6  illustrates an exemplary embodiment of a portable data cartridge; 
         FIG. 7  illustrates an exemplary embodiment of an automated removable cartridge storage device; 
         FIG. 8  illustrates a first exemplary embodiment of a system controller that may be included in a removable cartridge storage device; 
         FIG. 9  illustrates a second exemplary embodiment of a system controller that may be included in a removable cartridge storage device; 
         FIG. 10A  is a block diagram of exemplary components of a system controller; 
         FIG. 10B  is a block diagram of exemplary software operations of a system controller; 
         FIG. 11  illustrates an exemplary embodiment of a front view of a an automated removable cartridge storage device; 
         FIG. 12  is a flow diagram illustrating an exemplary method that may be performed by a removable cartridge storage device to process data commands; 
         FIG. 13  is a flow diagram illustrating an exemplary method that may be performed by a removable cartridge storage device to audit and/or maintain an inventory of portable data cartridges; 
         FIG. 14  is a flow diagram illustrating an exemplary method that may be performed by a removable cartridge storage device to process a move command; and 
         FIG. 15  is a flow diagram illustrating an exemplary method that may be performed by a removable cartridge storage device to process an exchange command. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without some of these specific details. In other instances, well-known structures and devices are shown in block diagram form. 
       FIG. 5A  illustrates an exemplary embodiment of a removable cartridge storage device  500 . The removable cartridge storage device  500  may include a system controller  502 , a cartridge interface  506 , and a cartridge holder  508 . A host computer system  520  may be communicatively coupled with removable cartridge storage device  500 . As will be described further below, portable data cartridges  510  may be removably coupled with removable cartridge storage device  500 . 
     System controller  502  may process data commands and other types of commands (or requests) transmitted to the removable cartridge storage device  500 . In some aspects, the system controller  502  may include an interface  504  to host computer  520 . Interface  504  may be used to receive device commands and data from host computer  520  and to transmit data and other communications from removable cartridge storage device  500  to the host computer  520 . By way of example, the interface  504  to the host computer  520  may be a any version of Small Computer System Interface (SCSI), a Fiber Channel (FC) interface, an Ethernet interface, an Advanced Technology Attachment (ATA) interface, or any other type of interface that allows the removable cartridge storage device  500  to communicate with a host computer  520 . System controller  502  may also perform other functions to process data, such as data buffering, data compression, error correction coding (ECC) and data formatting for the data cartridge  508  used to store data. Other well-known functions of a system controller, such as error recovery, may also be performed by system controller  502 . 
     In some embodiments, removable cartridge storage device  500  may emulate a tape device. In these aspects, system controller  502  may be configured to emulate a tape device and/or execute tape device commands (e.g., sequential tape device commands, such as any version of SCSI Stream Commands (SSC) or Advanced Technology Attachment Packet Interface (ATAPI commands). Hence, in some embodiments, data may be written to and read from portable data cartridge  508  sequentially. System controller  502  may translate tape device commands received from a host computer  510  into the appropriate commands for the removable cartridge storage device  500 . Some of the tape device commands may not result in any action by removable cartridge storage device  500  (other than possibly an acknowledgement or success communication result) if the tape device command does not have a corresponding command for portable cartridges with electrical interfaces (e.g., rewind). System controller may also emulate a tape device when it transmit results and other communications back to host computer  510 . Thus, the removable cartridge storage device  500  may appear to software applications (e.g., backup applications) running on the host computer  510  as a tape device. In alternative embodiments, the removable cartridge storage device  500  may appear to the host computer  510  as another type of storage device, such as a random-access block device (e.g., hard disk drive, optical disk drive, flash memory). 
     System controller  502  may be communicatively coupled with cartridge interface  506 . Cartridge interface  506  may comprise electronic circuits which may be used to provide the physical electronic signaling to a portable data cartridge  510  (removably coupled with cartridge holder  508 ) to read and write data and to issue commands to the portable data cartridge  508 . In one embodiment, the cartridge interface  506  may include a single port serial ATA (Advanced Technology Attachment). 
     Cartridge interface  506  may be communicatively coupled to a cartridge holder  508 , which may be configured to removably couple with a portable data cartridge  510 . Although  FIG. 5A  illustrates a data cartridge  510  inserted into the cartridge holder  508 , at times, a data cartridge will not be inserted into cartridge holder  508 . Additional data cartridges may also be used with the removable cartridge storage device  500 . 
     Removable cartridge storage device  500  may be designed so that a portable data cartridge  508  may be inserted by a user at any time, regardless of the power state or other state of host computer  510 . Other aspects may allow a data cartridge  508  to be ejected at the request of the user (e.g., by means of an eject button) and/or by command from an application, such as a software application executing on host computer  510 . System controller  502 , or other component, may include functionality to prevent the cartridge  508  from being ejected while a data transfer operation is in process. Prior art storage devices, such as Hard Disk Drives (HDDs), require the user to install and remove the device when the host computer is powered-off or by invoking special installation programs in the host computer or its operating system software. Unlike these types of devices, removable cartridge storage device  500  may enable portable data cartridges  508  to be asynchronously inserted without any user action with the host computer  510  or its operating software and without disrupting the operation of the host computer  510 , including its file system. 
     It should be appreciated that in alternative embodiments, the removable cartridge storage device  500  may include additional, fewer, or alternative components than shown in  FIG. 5A . For example, removable cartridge storage device  500  may include more than one interface, which may be the same or different than the type of interface  504 . Other variations are also contemplated. 
       FIG. 5B  illustrates an exemplary coupling between cartridge holder  508  and a portable data cartridge  510 . Cartridge holder  508  may include an electrical connector  530 . Data cartridge  510  may also includes an electrical connector  532  configured to mate with electrical connector  530 . Thus, data cartridge  510  may be electrically coupled to the removable cartridge storage device  500  via cartridge holder  508  by mating its electrical connector  532  with the electrical connector  530  of the cartridge holder  508 . 
     In other embodiments, cartridge holder  508  may removably couple and/or communicate with data cartridge  510  using different means. By way of example, cartridge holder  508  may use radio frequency, infra-red, or other types of wireless communications to communicate with data cartridge  510 . Thus, it should be appreciated that data cartridge  510  and cartridge holder  508  may include alternative or additional communications to enable data cartridge  508  to communicate with removable cartridge storage device  500 . 
       FIG. 6  illustrates one exemplary embodiment of a portable data cartridge  600  which may be used in a removable cartridge storage device. The data cartridge  600  may include an electrical connector  602  configured to mate the data cartridge  600  to the removable cartridge storage device. When the data cartridge  600  is coupled with a removable cartridge storage device, the removable cartridge storage device may read data from the cartridge, write data to the cartridge, and issue commands to the cartridge. The data cartridge  600  may store the data in portable electronic format, so that the data persists after the data cartridge  600  is removed from a removable cartridge storage device. The data may also be stored in a format so that it is readable by storage devices other than the storage device that wrote the data to the data cartridge  600 . 
     Data cartridge  600  may, in some aspects, include an embedded hard disk drive (HDD)  604 . HDD  604  may include functionality similar to a standard HDD. For instance, data may be stored on HDD  604  by issuing a write command to the data cartridge  600  via electrical connector  602 . Other known disk commands may also be issued to HDD  604  via the electrical connector interface  604 . 
     In some embodiments, data cartridge  600  may have functional characteristics similar to a tape cartridge, such as an ergonomic form and low cost. In other embodiments, data cartridge  600  may not include an embedded HDD  604 , but instead may include another type of data storage that has an electronic interface, such as optical or flash storage. Further details of features that may be included in data cartridge  600  may be found in previously incorporated provisional patent application No. 60/586,087, entitled “Electronic Storage Cartridge.” 
       FIG. 7  illustrates an exemplary embodiment of an automated removable cartridge storage device  700 . The automated removable cartridge storage device  700  may be coupled with a host computer  720  via one or more connections  722 ,  724 . In some aspects, connection  722  may be a data path connection used to transfer data and data commands/results and connection  724  may be a control path command used to transfer media changer commands/results. In other aspects, a single connection  722  may be used to transfer both data path and control path communications and connection  724  may not be included. Further details of both exemplary embodiments will be described below with reference to  FIGS. 8 and 9 . It should be appreciated that automated removable cartridge storage system  700  may also be coupled with additional host computer systems (not illustrated). 
     The automated removable cartridge storage device  700  include a system controller  702 . System controller  702  may be configured to receive and execute commands from host computer  720 . The commands received from host computer  720  may be data commands and/or media changer commands. System controller  702  may also perform any of the other functionality described with reference to the system controller  502  of  FIG. 5A . Additional details of the configuration and functionality that may be performed by system controller  702  are also described below. 
     The automated removable cartridge storage device  700  may also include a cartridge interface  704 , communicatively coupled with system controller  702 . Cartridge interface  704  includes electronic circuitry which may be used to provide electronic signaling to multiple portable data cartridges  714 ,  716 ,  718  having electronic interfaces. Portable data cartridges  714 ,  716 ,  718  may be removably coupled with cartridge holders  708 ,  710 ,  712  using any of the mechanisms described elsewhere in this application (e.g., through mating electrical connectors). As previously described, the data cartridges  714 ,  716 ,  718  may include an embedded HDD or other type of storage that may be electrically coupled with data replication system  700 . In alternate embodiments, the system  700  may include fewer or additional cartridge holders  708 ,  710 ,  712  to which a data cartridge  714 ,  716 ,  718  may be electrically coupled. 
     Cartridge interface  704  may also include a switch  706  or other type of electronic switching component, such as a multiplexer or other multi-port device, to electronically switch communication connections between system controller  702  and portable data cartridges  714 ,  716 ,  718  removably coupled with cartridge holders  708 ,  710 ,  712  by making, breaking, or routing electrical connections between system controller and each of the cartridge holders  708 ,  710 ,  712 . In some embodiments, cartridge interface  704  may comprise a multi-port serial-ATA (Advanced Technology Attachment) or multi-port serial SCSI controller. In larger systems (e.g., in systems greater than 8 cartridges), the system controller  702  may include multiple electronic components and processes to simultaneously manage a subset of the data cartridges  714 ,  716 ,  718 , each subset coupled to its own cartridge interface  704 . 
     In some embodiments, the automated removable cartridge storage device  700  may emulate a tape automation device (e.g., tape autoloader, tape library). Thus, system controller  702  or another component may provide the functionality to emulate the control path to a tape automation device used by applications to issue media changer commands to the automated removable cartridge storage device  700 . Media changer commands to perform system configuration and diagnostics may also be processed by system controller  702 . Merely by way of example, system controller  702  may emulate a SCSI tape autoloader device and may process any version of the SCSI media changer commands (e.g., Initialize Element Status, Read Element Status, Move Medium, Exchange Medium, etc). It should be appreciated that system controller  702  may also emulate other types of devices and may process other types of media changer commands. 
     Automated tape device commands that are received may be translated to the appropriate command for the automated removable cartridge storage device  700 . For instances, commands such as load and unload may be translated into commands that cause the cartridge interface  704  to electronically switch from one cartridge  714 ,  716 ,  718  to another cartridge. As other examples, audit commands (e.g., Initialize Element, Read Element Status) and/or move medium commands may be performed electronically by the system controller  702 . Exemplary methods that may be performed by a system controller  702  to process media changer commands are described below. 
     In embodiments in which the automated removable cartridge storage device  700  emulates an automated tape device, storage elements may be represented in the inventory by each of the cartridge holders  708 ,  710 ,  712 . Data transfer elements may be represented by the system controller (e.g., data formatter component) and its connection to a cartridge holder  708 ,  710 ,  712  via the cartridge interface switch  706 . The medium transport element may virtually be represented by the cartridge interface  704 , in which the electronic switching operation of the signal path between the system controller  702  and the cartridge holders  708 ,  710 ,  712  substitutes for the physical movement of data cartridges  714 ,  716 ,  718 . The import/export element may be virtually represented by the ejected state of the portable data cartridge  714 ,  716 ,  718  from its cartridge holder  708 ,  710 ,  712 . 
     System controller  702  may also emulate a tape device and process tape commands. Merely by way of example, system controller may receive and process any version of the SCSI Stream Commands. Data associated with sequential write commands may be sequentially written to portable data cartridges. Similarly, data associated with sequential read commands may be sequentially read from portable data cartridges. 
     In some aspects, system controller  702  may maintain an inventory of the portable data cartridges  714 ,  716 ,  718  which are removably coupled with the cartridge holders  708 ,  710 ,  712 . In aspects in which the storage device  700  emulates an automated tape device, the storage device may also maintain an element inventory which includes physical and logical addresses for the elements. The physical address may correspond to the physical configuration within the storage device system and the logical address may be the address used by the host computer when it issues media changer commands to the automated removable cartridge storage device  700 . In aspects in which the system controller has the ability to operate more than one portable data cartridge  714 ,  716 ,  718  at a time, multiple logical addresses may be assigned to the system controller. Some elements may have unchangeable addresses, such as the data transfer elements (system controller  702  connection to cartridge interface  708 ,  710 ,  712 ), medium transport element (virtually represented by switch  706 ), and import/export elements (virtually represented by eject state of data cartridge). The logical addresses for these unchangeable elements may always be associated with the same physical address. For other elements, such as the cartridge holders, the logical addresses associated with the cartridge holders  708 ,  710 ,  712  may be swapped (e.g., if a move medium or exchange medium command is received). It should be appreciated that the element inventory may also include the portable cartridge inventory, or the portable cartridge inventory may be maintained as a separate inventory. It should also be appreciated that the portable cartridge inventory and/or element inventory may be stored on a non-volatile memory (e.g., EEPROM) of system controller  702  or other component of storage device  700 . 
     A suitable housing structure may be used to hold multiple cartridge holders  708 ,  710 ,  712 . The structure may be designed so that an operator may have access to the cartridge holders to add and remove cartridges  714 ,  716 ,  718 . One exemplary housing structure will be described below in reference to  FIG. 11 . Alternately, a robotic mechanism may be employed to enter and remove cartridges from the housing structure. 
     In an alternate embodiment, the automated removable cartridge storage device  700  may take the place of one or more tape drives within an existing tape automation system, such as a tape autoloader or tape library. The data cartridges  714 ,  716 , and  718  may be mechanically loaded and unloaded into cartridge holders  708 ,  710 ,  712  from storage slots within the automation system by a robotic mechanism. Thus, the cartridges  708 ,  710 ,  712  may be sized and shaped so that they may be handled by the robotic mechanism. This may provide the ability for customers to use portable disk data cartridges or other type of removable cartridge having an electrical interface within existing tape systems. 
     It should be appreciated that automated removable cartridge storage device  700  may provide capabilities not available in traditional autoloader devices or tape libraries having multiple tape drives. Unlike traditional automation systems, the storage device  700  may electronically, instead of mechanically, switch between cartridges. Thus, storage device  700  may be able to switch cartridges much more rapidly (e.g., less than one second) than traditional automated systems that mechanically move cartridges. Additionally, unlike virtual tape systems, the storage device  700  may be used with portable data cartridges that retain data after removal from the storage device  700  and may be read by other storage device systems. System controller  702  may also operate each portable data cartridge independently of the other portable data cartridges. In some cases, each portable data cartridges  714 ,  716 ,  718  may include its own independent data set. In other aspects, portable data cartridges  714 ,  716 ,  718  may be formatted in a RAID format, as described further below. 
     Another capability that may be provided by automated removable cartridge storage device  700  is a single system controller that may be used to control data operations for multiple data cartridges. Thus, data may be copied from one data cartridge  714  to a second data cartridge  716  using the single system controller  702  without the need to first transfer the data to the host computer. The use of a one system controller  702  may also allow sequential load and copy functions to be performed in parallel, thereby providing the functions of an autoloader and a mirroring system with a single controller. For instance, the system controller  702  may be able to operate all of the cartridges  714 ,  716 ,  718  close to simultaneously by bursting data to a data cartridge  714 ,  716 ,  718  and then electronically switching to a different cartridge while the first data cartridge processes the burst data. Other capabilities may also be provided by storage device  700  which uses a single system controller  702  to manage-multiple removable data cartridges  714 ,  716 ,  718 . 
       FIG. 8  illustrates an exemplary embodiment of components that may be included in a system controller of an automated removable cartridge storage device. System controller  800  includes a host interface  802 , such as a SCSI, FC, Ethernet, or other type of communications interface. Host interface  802  may be used to send and receive media changer communications to and from a host computer. In one embodiment, media changer communications may be a standardized communication protocol, such as any version of the SCSI Media Changer command set (e.g., SCSI-3 Media Changer command set). Other communication protocols may also be used. 
     System controller  800  also includes an additional host computer interface  804  (SCSI, FC, etc.) which may be used to receive data and commands to control the transfer/formatting of data from a host computer. Host computer interface  804  may also be used to transfer data (e.g., for restore operations) and results of data operations from the system controller  800  to the host computer. Merely by way of example, host computer interface  804  may be any version of SCSI, a Fiber Channel interface, an Ethernet interface, an ATA interface, or any other type of interface that may be used to transfer data and data command communications. It should be appreciated that the host computer may either be the same or different host computer than that communicating with host computer interface  802 . 
     Functionality performed by system controller  800  may be logically partitioned into a media changer controller (MCC)  806  and data controller/formatter  808 . MCC  806  is communicatively coupled with host computer interface  802 . MCC  806  may be used to process media changer commands, such as audit commands, commands to electronically switch between data cartridges, or any other type of media changer command. Data controller  808  is communicatively coupled with host computer interface  804  and may be used to control data transfers and formatting of data. By way of example, data formatting operations performed by data controller  808  may include block packing, data compression, header creation, or other formatting to prepare data for recording on one or more cartridges in a native format of the cartridge. System controller  800  may optionally include a data buffer (not shown) that may be used by data controller  808  during transfer/formatting operations. 
     In some embodiments, MCC  806  may be used to emulate an automated tape device (e.g., autoloader, tape library). Media changer commands received from a host computer may thus be translated by MCC  806  into the appropriate commands (if any) for the automated removable cartridge storage device and translate results into the format expected by host computer. By way of example, MCC  806  may process a load command by electrically switching the switch to the appropriate cartridge. In some cases, data controller  808  may also emulate a tape drive, optical drive, or other type of device. 
     It should be appreciated that  FIG. 8  illustrates an exemplary logical partitioning of functionality performed by system controller  800 . MCC  806  and data controller  808  may be components of the same or different processor and may be implemented as one or more embedded software processes. It should also be appreciated that system controller  800  may include additional components. 
       FIG. 9  illustrates a second exemplary embodiment of components that may be included in a system controller of an automated removable cartridge storage device. This embodiment is similar to that described with reference to  FIG. 8 , with the difference being that a single host computer interface  902  is shared by both media changer controller  904  and data controller  906 . 
       FIG. 10  illustrates another exemplary embodiment of components that may be included in a system controller. The system controller  1000  includes a host interface  1002 , such as a SCSI, FC, Ethernet, or other type of communications interface. The host interface  1002  may be used to send and receive communications from a host computer. Host interface  1002  is coupled to a data buffer  1006  that may be used to store incoming and outgoing data. By way of example, data buffer  1006  may be dynamic random access memory (DRAM). Other types of memory may also be used. 
     System controller  1002  further includes a processor  1004  which may be used to process data (e.g., format data, compress data, etc.) and manage communications and data transfers to the data cartridges. The components of system controller  1002  may be implemented as a combination of electronic circuits, a microprocessor, and embedded software which runs on the microprocessor and operates the circuitry. It should be appreciated that in alternate embodiments, the system controller  1002  may include different components than those described with reference to  FIG. 10A . For instance, in some embodiments, the system controller  1002  may include additional host interfaces  1002  to allow communications with more than one host computer or to receive media changer commands from host computer. 
       FIG. 10B  illustrates an exemplary block diagram of embedded software processes that may be performed by system controller  702  when receiving data and data commands from a host computer. Host interface process  1010  may be used to receive data commands and data transfers and put them in the input section  1020  of data buffer  1006 . In some aspects, host interface process  1010  may also be used to receive media changer commands, some of which are translated to control a cartridge interface to virtually load and unload portable data cartridges by operating an electronic switching mechanism. In some embodiments, host interface process  1010  may emulate an automated tape device, such as a tape autoloader or tape library and/or a tape device. 
     Data formatting process  1012  may be used to remove data from the input section  1020  of the data buffer  1006  and perform formatting operations on the data. By way of example, data formatting process may perform block packing, data compression, header creation, and/or other formatting to prepare the data for recording on one or more portable cartridges in a native format of the cartridges. 
     In some embodiments, data formatting process  1012  or another process of system controller  1000 , may be used to format the data in a Redundant Array of Inexpensive Disks (RAID) format for transfer to the number of data cartridges needed to support the selected RAID format. The use of a RAID format may provide for additional fault tolerance for data restoration. In the event that one of the data cartridges used in the RAID becomes corrupted, the remaining cartridges in the array may store enough information so the data may still be restored. Thus, the data cartridges may form a redundant set of independent disk cartridges (RAID-RC), in which a variety of RAID formats (e.g., RAID-3, RAID-5, RAID-6) may be used. After the data formatting process  1012  has finished formatting the data, the data may be sent to the output section  1022  of the data buffer  1006 . The cartridge interface process  1014  may then remove the formatted data as needed to manage the communication and data transfer to a data cartridges  714 , 716 ,  718 . In some embodiments, more than one cartridge interface process  1014  may be provided to transfer data in parallel to data cartridges. 
     Although the above description described the functionality performed by system controller  1000  when data and commands are received from host computer, it should be appreciated that similar functionality in reverse may be performed by the processes to send data to the host computer. For instance, host interface process  1010  may retrieve data from data buffer  1006  for transmittal to the host computer. As another example, the data process  1012  may also be used to de-format data for transmittal to the host computer, as well as performing other types of data operations (e.g., uncompressing data) for transmittal to the host computer. Additionally, cartridge interface process  1014  or other process may be used to receive data read from data cartridges during read operations. In alternative embodiments, the system controller  1000  may include fewer, different, or additional processes to manage data transfers between host computer and data cartridges removably coupled with the storage device. 
       FIG. 11  illustrates a front view of an exemplary embodiment of an automated removable cartridge storage device  1100 . The device  1100  includes a plurality of cartridge holders  1101 - 1108  for receiving removable cartridges. Each cartridge holder  1101 - 1108  may define an opening exterior to the removable cartridge storage device  1100  to receive a portable data cartridge. In some aspects, the cartridge holders  1101 - 1108  may each have an associated eject button  1111 - 1118  for ejecting the cartridge from the cartridge holder. Additionally, in some embodiments, status indicators (not shown), such as light emitting diode (LED) status indicators, may also be provided for each cartridge. The removable cartridge device  1100  may further include a control panel interface  1120  to display autoloader device information, configure the storage device  1100 , power on/off the autoloader, and/or reset the device  1100 . 
     In the embodiment illustrated in  FIG. 11 , the location of the cartridge holders  1101 - 1108  on the front panel may make it easy for an operator to insert or remove cartridges. Thus, unlike prior art tape autoloaders with an single import/export mechanism feature, an operator of removable cartridge storage device  1100  may insert or remove as many cartridges as desired without repeatedly performing a sequence of control panel keystrokes. Instead, the operator may merely insert or plug the data cartridges into the cartridge holders  1101 - 1108  or press the associated eject button  1111 - 1118  to eject a cartridge. Thus, the removable cartridge storage device  1100  may, in effect, provide multi-cartridge import-export functionality. In alternative embodiments, one or more of the cartridge holders  1101 - 1108  may not be included on the front panel and the removable cartridge storage device  700  may provide another mechanism (such as a conventional import/export mechanism) to insert and remove cartridges into the device  700 . 
     It should be appreciated that in alternate embodiments, the automated removable cartridge storage device  1100  may include additional or fewer cartridge holders  1101 - 1108 . Additionally, in alternate embodiments, the device  800  may include fewer or additional components than shown in  FIG. 11 . 
       FIG. 12  illustrates an exemplary method that may be performed by a system controller or other component of a removable cartridge storage device to process data commands. The method may begin by receiving  1202  a data command from a host computer coupled with the removable cartridge storage device. The data command may be a data transfer command or other type of command associated with data transfer operations. Merely by way of example, the data command may be a read command, a write command, a copy command, or a medium movement command (e.g., rewind, seek). 
     In some embodiments, the removable cartridge storage device may emulate a tape device. In these embodiments, the received  1202  data command may be a sequential tape command (e.g., a SCSI Stream Commands) or other type of tape command. The system controller, or other component, may translate  1204  the command into a command suitable for the electronic medium of the portable data cartridges. For instances, a rewind or other movement command may be translated into a seek command or other appropriate command. Other types of commands may also be translated  1204  into a different type of command for the portable data cartridges and/or removable cartridge storage device. Some commands may not result in any action by the removable cartridge storage device (other than possibly reporting results), as the command my not have an equivalent command associated with the portable data cartridge. Furthermore, the action associated with some commands may be delayed until a subsequent command is received. By way of example, a seek command may not be executed until a subsequent write or read command is received. It should be appreciated that in alternative embodiments, the method may not include translating  1204  the data command. 
     At some point, the system controller may cause a cartridge interface component of the storage device to electronically  1206  switch communications to the target data cartridge. The switching  1206  to the target cartridge may occur before the data command is received  1202 , immediately before executing  1208  the command, and/or after receiving a subsequent data command  1202 . Merely by way of example, communications between the system controller and the portable data cartridges may have been switched in response to a load or move command previously received. As another example, the received  1202  command may be a data operations command (e.g., read, write, copy) or other type of command for which the system controller causes the switch to switch communications to the target cartridge (data source and/or destination) prior to executing the data operation command. In some aspects, this may occur immediately before executing  1208  the data operation or a portion of the data operation. Other types of data commands, such as media movement commands (e.g., rewind, seek, etc.) may not be immediately executed  1208  until a subsequent command (e.g., a data operations command) is received. Thus, the system controller may not electronically switch  1206  to the target cartridge until after the subsequent command is received. 
     At block  1208 , the data command is executed  1208 . In some aspects, a sequence of commands may be executed  1208  (e.g., a seek command or other move media command followed by a read command or other data operations command). Optionally, the system controller may execute  1208  the command simultaneously with other commands for different target cartridges. For some types of commands, the system controller may perform data formatting (e.g., block packing, data compression, header creation), de-formatting, data compression, data uncompression, and/or data buffering while executing  1208  the command. Thus, it should be appreciated that the system controller may cause the switch to electronically switch  1206  to the target cartridge multiple times during the execution  1208  of the command. 
     One example of a data command that may be executed  1208  by removable cartridge storage device is a copy command. Unlike traditional data storage devices, the removable cartridge storage device may be able to execute the copy command without first transferring the data to be copied to the host computer. Instead, the system controller may read the data from the source data cartridge, electronically switch to the destination data cartridge, and write the data to the destination data cartridge directly from its data buffer. Thus, the copy operation may be able to be performed more quickly and efficiently than a traditional storage device. 
     At block  1210 , the removable cartridge storage device may transmit  1210  a result and/or data to the host computer. In some instances, the removable cartridge storage device may transmit a success result even though the execution of the command has been delayed to a later time. For example, in embodiments in which the storage device is emulating a tape device, the removable cartridge storage device may transmit  1210  a success result for a media movement command, even though the corollary command for the electronic data cartridges has not yet been executed. 
       FIG. 13  illustrates an exemplary method that may be performed by a removable cartridge storage device to audit and/or maintain an inventory of portable data cartridges. The audit may be initiated when the removable cartridge storage device is powered on or reset. Alternatively, the audit may be initiated by receiving a command from a host computer (e.g., Initialize Element Status, or other type of audit command) or a user directly interacting with a control panel of the removable cartridge storage device. 
     The audit process may begin by reading  1302  an inventory saved in a memory of the storage device. The inventory may include address for the elements included in the storage device. In some embodiments, the inventory list may include both physical addresses and logical addresses used by host computer(s) when it issues commands to the storage device. In other embodiments, the mappings between the physical and logical addresses may be maintained in a separate inventory list or may not be used. In some cases, data cartridges in the inventory list may be associated with one or more elements. For example, in embodiments in which the storage device emulates an automated tape device, a data cartridge may be associated with both the cartridge holder element to which it is removably coupled and a data transfer element (virtually represented in the storage device by a connection between the system controller and a cartridge holder). 
     If the storage device has not been previously audited, the removable cartridge storage device may create the initial inventory list instead of reading  1302  an inventory in saved memory. Alternatively, an empty inventory list may be read from memory. The empty inventory list may not include any data cartridges, but instead may include the physical addresses of the cartridge interfaces and in some embodiments, the logical addresses associated with addresses used by host computer(s) communicating with the storage device and addresses of other elements virtually represented in the removable cartridge storage device. 
     At block  1304 , the removable cartridge storage device scans the cartridge holders to determine the presence of a data cartridge. The label of the data cartridge may also be determined. Any suitable technique may be used to scan  1304  the cartridge interfaces. For example, the system controller or other component of the storage device may determine the presence of a data cartridge by electronically reading a sensor associated with the cartridge holder. Alternatively, the system controller (or other component) may attempt to communicate with each of the cartridge interface to determine if a data cartridge is coupled with the cartridge interface. Unlike traditional storage devices relying on mechanical means to perform audits, the removable cartridge storage device may perform the audit by scanning  1304  the cartridge holders electronically, instead of mechanically. Thus, the audit of the storage device may be performed more quickly than traditional storage systems 
     A cartridge holder may include information different than the saved inventory list if a user changed, added, or ejected cartridges while the storage device was powered down or otherwise inoperable. If the status of a cartridge holder has changed from the saved inventory, the inventory is updated with the new information. The updated inventory is saved  1306  to the memory of the storage device. The inventory list may then be used to process subsequent commands from the host computer to retrieve the inventory or partial inventory (e.g., Read Element Status). 
     In order to keep the inventory up to date, the removable cartridge storage device may execute a background process or other type of process to monitor the cartridge holders  1308 . If an insertion of a cartridge is detected  1310 , the new cartridge is added to the inventory list and the updated inventory is saved  1306 . If the system controller, or other component, detects that an eject button was pressed  1314 , the cartridge may be removed  1318  from the inventory list and the updated inventory list may be saved  1306 . Optionally, the system controller may control eject operations in order to help prevent cartridges from being ejected during data transfer operations. In these embodiments, the system controller may also cause an eject mechanism to be operated  1316  to permit the ejection (assuming data transfer operations are not taking place or the data transfer operation has concluded). 
       FIG. 14  illustrates an exemplary method that may be performed by a removable cartridge storage device to process a move command. At block  1402 , a move command is received  1402 . A move command may be received  1402  in embodiments in which the storage device is emulating an automated tape device. Merely by way of example, the move command may be any version of the SCSI Move Medium command. In other aspects, the move command may be another type of SCSI move command (e.g., a move command directing a robotic tape library to move cartridges), a Fiber Channel move command, or other type of move command issued to an automated tape device. Alternatively, the received move command may be a virtual move command directing the storage device to electronically switch communications to a target data cartridge (virtually move cartridge to data transfer mechanism), virtually move the target data cartridge to an import/export mechanism (which may enable the eject mechanism), or other type of virtual move command. In these embodiments, the storage device may not be emulating an automated tape device. Additional embodiments may also implement move commands. It should be appreciated that in further embodiments, the removable cartridge storage device may not implement or process move commands. 
     The received  1402  command may be parsed  1404  to determine the source element for the move command and the destination element for the move command. The source or destination element may be a cartridge holder (storage element), a data transfer element (virtually represented by a communication connection between the system controller and a data cartridge), an import/export element (virtually represented by an entered/ejected state of the cartridge and/or enablement of an eject mechanism associated with the cartridge), or other types of element that may be included in the removable cartridge storage device. In alternative embodiments, the move command may include additional or alternative parameters than source/destination elements. For instances, the move command may specify a data cartridge instead of a source element. Thus, alternative, additional, or fewer parameters may be parsed  1404  from the move command. 
     If  1406  any of the required parameters are not present (e.g., source/destination elements), an error message is transmitted  1410  to the host computer. For instances, the source/destination elements may not be present if the host computer incorrectly identified an element and/or has an invalid configuration for the removable cartridge storage device. As another example, an error message may be transmitted  1410  to the host computer if a cartridge parameter specified in the move command is not present. 
     At block  1408 , a determination is made as to whether the destination element for the move command is available. A determination  1408  may be made that a destination element is not available in a variety of different circumstances. For instances, the storage device may determine a data transfer element is not available if the system controller is busy transferring data or reading data from another data cartridge. As another example, the storage device may determine an element is not available if it is occupied by another cartridge. Even though the removable cartridge storage device may be able to virtually move cartridges to an occupied element (e.g., by swapping the cartridge&#39;s logical addresses), this may result in inconsistencies between the inventory maintained by the host computer and the inventory maintained by the storage device. Thus, the host computer may inadvertently issue commands associated with data cartridge(s) other than the intended data cartridge(s) intended to be associated with the command. In alternative embodiments, this may not be a consideration and/or may be addressed in a different manner, and thus, the removable cartridge storage device may determine  1408  the destination element is available even if it is occupied. The storage device may also determine the destination element is not available in other circumstances. If the storage device determines  1408  the destination element is not available, it may transmit  1410  an error message to the host computer. 
     Otherwise, the host computer may proceed with processing the move command. The move command may be processed differently, depending upon the targeted destination element. If  1412  the target destination element is a data transfer element, a cartridge interface may be operated to switch  1414  an electronic connection from the system controller to the desired cartridge (located in the source element or specified in the move command). At block  1424 , the inventory may be updated to reflect the data transfer element virtually represented by the connection between the system controller and a cartridge interface has been changed. In some embodiments, the inventory may reflect the cartridge occupies both a data transfer element and a cartridge holder (storage element). In these aspects, the inventory may reflect the logical address of the cartridge holder is available. 
     If  1416  the target destination is an import/export (eject) mechanism, the storage device may operate  1418  an eject mechanism to allow an operator to remove the cartridge. Alternatively, no action may be taken as the operator may be allowed to press an eject button or other type of mechanism to remove the cartridge at any time, or the eject mechanism may not be operated until an operator presses the eject button. The removable cartridge storage device may also update  1424  its inventory to remove the ejected cartridge from the inventory. 
     If  1420  the target destination element is another storage element, the storage device may swap  1422  the logical address used by the host computer for the source cartridge holder with the logical address used by the host computer for the destination cartridge holder. The storage device inventory  1424  may also be updated to reflect this change. 
     Other suitable actions may alternatively or additionally be performed by the removable cartridge storage device to execute the move command. It should be appreciated that the time required to complete the move operation may be nearly instantaneous since the move operation may be completed electronically. Thus, removable cartridge storage device may provide a significant advantage over conventional mechanical storage systems which take tens of seconds to perform move operations. 
     Variations to the method described above are contemplated. For example, in some embodiments, the removable cartridge storage device may implement a physical import/export element(s) to import/export cartridges into the device and/or physical storage elements may be locations in the storage device which are not in communication with the system controller. Thus, the receipt of a move command may result in physical movement of the cartridge. As another example, the removable cartridge storage device may implement a physical cartridge mover (e.g., to move cartridges from storage elements not connected to the switch to elements that are connected to the switch). Thus, in some instances, the move command may be executed physically instead of electronically. Other variations are also contemplated. 
       FIG. 15  is a flow diagram illustrating an exemplary method that may be performed by a removable cartridge storage device to process an exchange command. An exchange command may be a special type of move command where the contents of two elements are swapped. In some aspects, the exchange command may be a command for an automated tape device, such as a SCSI Exchange Medium command or other type of command to swap the contents of elements in an automated tape device. In other embodiments, the command may not be a command executable by an automated tape device. 
     At block  1502 , the exchange command is received. The command is then parsed  1504  to obtain the parameters associated with the command. By way of example, a source element and a destination element may be obtained from the parsing. 
     The action(s) taken to process the command may depend upon the type of elements involved in the command. If  1506  the exchange command is between a storage element and a data transfer element (virtually represented by an electronic connection between system controller and a cartridge interface), a determination may be made as to whether the data transfer element is available  1508 . The data transfer element may not be available if the system controller is busy processing another data transfer operation. Thus, an error message  1410  may be transmitted to the host computer. Other circumstances may also result in a determination  1508  that a data transfer element is not available. 
     If  1508  the data transfer element is available  1508  and if  1512  there is not another cartridge assigned to the data transfer element, the system controller, or other component of the storage device, may cause the cartridge interface to electronically switch  1516  communications from the system controller to the cartridge holder associated with the second exchange element and the inventory may be updated  1526 . Otherwise, if  1508  the data transfer element is available and if  1512  there is another cartridge assigned to the data transfer element, the storage device may swap the logical address associated with the cartridge already assigned to the data transfer element with the logical address of the swapped cartridge. The cartridge interface is also switched  1516  to the cartridge holder to which the swapped cartridge is removably coupled and the inventory is updated  1526 . In alternative embodiments, if  1512  there is another cartridge assigned to the data transfer element, an error message may be transmitted to the host computer. 
     If  1518  the source and destination elements of the exchange command are storage elements (cartridge holders), the storage device may swap  1520  the logical addresses associated with the physical addresses of the cartridge holders. Thus, the logical addresses used by the host computer will correspond to the physical addresses of the cartridge interfaces after the cartridges have been “virtually” swapped. At block  1526 , the inventory is updated to reflect the changed logical addresses. 
     If  1522  the destination address is a virtual import/export mechanism, the exchange command may be processed by operating  1524  an eject mechanism and updating  1526  the inventory to remove the ejected cartridge. In other embodiments, the eject mechanism may not be operated  1524  until an operator presses an eject button associated with the cartridge holder. 
     In alternative embodiments, variations may be made to the method described in  FIG. 15 . Merely by way of example, in some embodiments, the removable cartridge storage device may implement a physical cartridge mover and/or a physical import/export mechanism. Thus, the exchange command may be processed using physical movements instead of or in addition to virtual exchanges. 
     In the foregoing description, for the purposes of illustration, methods were described in a particular order. It should be appreciated that in alternative embodiments, the methods may be performed in a different order than that described. Additionally, the methods may include additional, different, or fewer blocks than described. It should also be appreciated that the methods may be performed by hardware components or may be embodied in sequences of machine-executable instructions, which may be used to cause a machine, such as a general-purpose or special-purpose processor or logic circuits programmed with the instructions to perform the methods. These machine-executable instructions may be stored on one or more machine readable mediums, such as ROMs, RAMs, EPROMs, EEPROMs, magnetic or optical cards, flash memory, or other types of machine-readable mediums suitable for storing electronic instructions. Alternatively, the methods may be performed by a combination of hardware and software. 
     While illustrative and presently preferred embodiments of the invention have been described in detail herein, it is to be understood that the inventive concepts may be otherwise variously embodied and employed, and that the appended claims are intended to be construed to include such variations, except as limited by the prior art.