Abstract: The disk controller has a plurality of channel control units, a plurality of cache memories, a plurality of disk control units, and a plurality of internal switch units. Each channel control unit or disk control unit sends to one of the cache memory units a request packet requesting execution of processing. The cache memory unit sends a response packet in response to the received request packet. Each internal switch unit monitors the request packet sent from the channel control unit or disk control unit, and judges whether or not the response packet to the request packet has passed through the internal switch unit within a first given time period since the passage of the request packet. In the case where the response packet has not passed through the internal switch unit within the first given time period, the internal switch unit sends a failure notification.

Abstract: Multiple Array Management Functions (AMFs) are connected to multiple redundancy groups over a storage area network (SAN), such as a fiber-channel based SAN. The multiple AMFs share management responsibility of the redundancy groups, each of which typically includes multiple resources spread over multiple disks. The AMFs provide concurrent access to the redundancy groups for associated host systems. When a host requests an AMF to perform an operation on a resource, the AMF synchronizes with the other AMFs sharing control of the redundancy group that includes the resource to be operated on, so as to obtain access to the resource. While performing the operation, the AMF send replication data and state information associated with the resource such that if the AMF fails, any of the other AMFs are able to complete the operation and maintain data reliability and coherency.

Abstract: A distributed data storage system breaks data into n slices and k checksums using at least one matrix-based erasure code based on matrices with invertible submatrices, stores the slices and checksums on a plurality of storage elements, retrieves the slices from the storage elements, and, when slices have been lost or corrupted, retrieves the checksums from the storage elements and restores the data using the at least one matrix-based erasure code and the checksums. In a method for ensuring restoration and integrity of data in computer-related applications, data is broken into n pieces, k checksums are calculated using at least one matrix-based erasure code based on matrices with invertible submatrices, and the n data pieces and k checksums are stored on n+k storage elements or transmitted over a network.

Abstract: Disclosed is a method of managing a non-volatile memory device having a plurality of memory blocks which includes assigning the plurality of memory blocks of the non-volatile memory device into a user data area and a writable area; determining whether any of the plurality of memory blocks of the nonvolatile memory device are runtime bad blocks; and replacing each determined runtime bad block from among the plurality of memory blocks with a memory block of the writable area.

Abstract: Availability of an information system including a storage system that performs remote copy between two or more storage apparatuses and a host computer using such storage system is improved. A third storage apparatus including a third volume is coupled to a first storage apparatus, a fourth storage apparatus including a fourth volume is coupled to a second storage apparatus, the first and third storage apparatuses perform remote copy of copying data stored in a first volume to the third volume, the first and second storage apparatuses perform remote copy of copying data stored in the first volume to a second volume, and the third and fourth storage apparatuses perform remote copy of copying data stored in the third volume to the fourth volume.

Abstract: A system and method for data storage in an array. A system includes a client coupled to a storage subsystem including data storage locations addressable as rows and columns in an array. Each column comprises a separate storage device. Each row includes redundant data. For a given row, a coordinating storage device coordinates the computation and storage of redundant data. The system detects a failure of a storage region and in response, configures an overlay storage device to temporarily overlay the failed region, maintains an association between the overlay device and the failed region, and maintains a record of changes made to the overlay device while the region is in a failed state. In response to detecting that the failed region has been restored, the system uses the association to identify the overlay device and uses the record of changes made to the overlay device to resynchronize the failed region.

Abstract: A memory profiling system profiles memory objects in volatile memory and identifies memory objects as candidates to be stored and read directly from nonvolatile memory. The profiling system monitors memory accesses via page faults and identifies a memory object to be loaded in volatile memory. The profiling system uses page faults to determine a page fault type and a write frequency for the memory object, and determines the memory object's memory access type. The profiling system determines whether the object's memory access type meets the capabilities of the nonvolatile memory technology. If the memory access type meets the nonvolatile memory technology capabilities, the profiling system identifies the memory object as a candidate to be transitioned to and read directly from nonvolatile memory (e.g., NOR and PCM). The profiling system stores the memory object candidates in nonvolatile memory such that the memory objects are read directly from nonvolatile memory.

Abstract: A memory system includes a memory controller, one or more memory channel(s), and a memory subsystem having a memory interface device (e.g. a hub or buffer device) located on a memory subsystem (e.g. a DIMM) coupled to the memory channel to communicate with the memory device(s) array. This buffered DIMM is provided with one or more spare chips on the DIMM, wherein the data bits sourced from the spare chips are connected to the memory hub device and the bus to the DIMM includes only those data bits used for normal operation. The buffered DIMM with one or more spare chips on the DIMM has the spare memory shared among all the ranks, and the memory hub device includes separate control bus(es) for the spare memory device to allow the spare memory device(s) to be utilized to replace one or more failing bits and/or devices within any rank of memory in the memory subsystem.

Abstract: The invention provides a method of managing bad block in a data storage device having an OTP memory die in order to present a continues address space toward the user, by using some of the OTP memory space for the management and maintaining address replacement table. Fast and efficient programming and writing algorithms are presented.

Abstract: A computer system wherein, when a state of the primary host computer is in an active state, a data sent from the primary host computer to the first storage system is copied through a first copy route which includes a route from the first storage system to the second storage system and a route from the second storage system to the third storage system, wherein, if a failure occurs in the primary host computer and a state of the second host computer is to be in an active state, a data sent from the secondary host computer to the second storage system is copied through a second copy route which includes a route from the second storage system to the first storage system and a route from the first storage system to the third storage system.

Abstract: Fault tolerant operation is disclosed for a primary match server of a financial exchange using an active copy-cat instance, a.k.a. backup match server, that mirrors operations in the primary match server, but only after those operations have successfully completed in the primary match server. Fault tolerant logic monitors inputs and outputs of the primary match server and gates those inputs to the backup match server once a given input has been processed. The outputs of the backup match server are then compared with the outputs of the primary match server to ensure correct operation. The disclosed embodiments further relate to fault tolerant failover mechanism allowing the backup match server to take over for the primary match server in a fault situation wherein the primary and backup match servers are loosely coupled, i.e. they need not be aware that they are operating in a fault tolerant environment.

Abstract: A link table recovery method for a flash memory having a plurality of blocks is provided. The method includes: selecting one block from the blocks; selecting a last page containing data of the selected block; checking the last page to determine whether the last page has errors; moving the correct data in the selected block to one of the spare blocks when the last page of the selected block detects errors; and updating a link table of the flash memory.

Abstract: A block management and replacement method for a flash memory is provided. The method includes grouping physical blocks of the flash memory into physical units and dividing the physical units as a usage area and a replacement area, wherein the physical blocks grouped into the same physical unit are accessed by using a multi-planes accessing command. The method also includes when one of the physical block of the physical unit in the usage area is damaged, replacing the physical unit having the damaged physical block with one physical unit selected from the replacement area and recording the undamaged physical block within the replaced physical unit if there is an applicable physical unit in the replacement area; and replacing the damaged physical block with one physical block selected from the replacement area if there is no applicable physical unit but an undamaged physical block in the replacement area.

Abstract: A method for rapid restarting of a flight control system, wherein the flight control system comprises a processor, is provided. The method includes storing at least one executable program on a memory device and copying the at least one executable program to a first random access memory (RAM) sector and a second RAM sector of a RAM memory device at a predetermined time. The method also includes copying the at least one executable program from the second RAM sector to the first RAM sector upon a restart of the processor and reinitializing processor operation by executing the at least one executable program copied from the second RAM sector to the first RAM sector.

Abstract: In an embodiment, an apparatus is provided that may include circuitry to generate, at least in part, and/or receive, at least in part, at least one access request involving a redundant array of independent disks (RAID) storage. The storage may be capable of accessing, in response, at least in part, to the at least one request an encryption and/or parity information. The encryption may be of at least one portion of the data and/or the parity information. The encryption may be stored in (1) encrypted disk stripes in the storage such that the data is unrecoverable based solely upon remaining unencrypted portion of the data and the parity information stored in the storage, and/or (2) one or more respective disk stripes having a number that is determined based at least in part upon one or more encryption levels, if any, associated with at least one characteristic of the data.

Abstract: A memory chip having a memory with a plurality of non-redundant memory lines and a plurality of redundant memory lines, and a controller configured to allocate dynamically a redundant memory line to a failed memory line during runtime.

Abstract: Systems and methods for recovering from a fault in an array of data storage devices are provided. Fault recovery includes determining that a first data storage device of the array of data storage devices is more likely to fail that other storage devices of the array of data storage devices. A second data storage device in the array of data storage devices is selected to be used in recovering from a failure of the first data storage device. Data from the first data storage device is stored at the second storage device. In the event of a failure at the first data storage device, data storage operations are performed using the second storage device.

Abstract: Disclosed is a method of improving storage reliability comprising receiving an indicator of an impending failure of a first storage device in a RAID group. In response to the indicator, writing data to the first storage device is ceased. A first block of data directed to be written on the first storage device is written to a memory device. Data stored on the first storage device is copied to a second storage device. The first block of data is copied from the memory device to the second storage device. The RAID group is operated with the second storage device functioning in place of the first storage device. Data is read from said second storage device.

Abstract: Systems and methods, including computer software, for reading data from a flash memory cell involve detecting voltages from a group of memory cells. The group of memory cells have associated metadata for error detection, and each memory cell stores a voltage representing a data value selected from a plurality of possible data values. Each possible data value corresponds to one range of multiple non-overlapping ranges of analog voltages. Memory cells having uncertain data values are identified based on the detected voltages. Alternative data values for the memory cells having the uncertain data values are determined. A combination of alternative data values is selected, and an error detection test is performed using the metadata associated with the memory cells and the selected combination of alternative data values.

Abstract: A network storage server implements a method to perform transactional failover of data sets. Multiple storage objects are organized into primary and secondary data sets, and a disaster recovery policy is configured for failing-over a primary data set to a secondary data set. A failover operation is defined for the disaster recovery policy. The failover operation includes multiple failover actions. During a failover situation, the failover operation is invoked to fail-over the primary data set. The failover operation is transactionally processed to ensure that all failover actions of the failover operation are performed in a single transaction.

Abstract: A network storage appliance is disclosed. The appliance includes a chassis enclosing a backplane, and a server enclosed in the chassis and coupled to the backplane. The appliance also includes storage controllers enclosed in the chassis, each coupled to the backplane, which control transfer of data between the server and storage devices coupled to the storage controllers. The storage controllers also control transfer of data between the storage devices and computers networked to the appliance and external to the appliance. The storage controllers and the server comprise a plurality of hot-replaceable blades. Any one of the plurality of blades may be replaced during operation of the appliance without loss of access to the storage devices by the computers. In one embodiment, the server executes storage application software, such as backup software for backing up data on the storage devices, such as to a tape device networked to the server.

Abstract: A disk drive system and method capable of dynamically allocating data is provided. The disk drive system may include a RAID subsystem having a pool of storage, for example a page pool of storage that maintains a free list of RAIDs, or a matrix of disk storage blocks that maintain a null list of RAIDs, and a disk manager having at least one disk storage system controller. The RAID subsystem and disk manager dynamically allocate data across the pool of storage and a plurality of disk drives based on RAID-to-disk mapping. The RAID subsystem and disk manager determine whether additional disk drives are required, and a notification is sent if the additional disk drives are required. Dynamic data allocation and data progression allow a user to acquire a disk drive later in time when it is needed. Dynamic data allocation also allows efficient data storage of snapshots/point-in-time copies of virtual volume pool of storage, instant data replay and data instant fusion for data backup, recovery etc.

Abstract: Disclosed is a method, system, and computer readable medium for restoring a failed non-volatile memory (NVM) system in a wireless device having a primary NVM system and a secondary NVM system. The method does not require a reboot of the wireless device. A NVM manager application detects a failure in either of the NVM systems and determines which NVM system has failed. If the primary NVM system has failed then the NVM manger switches the wireless device to operate using the secondary NVM system, restores the primary NVM system using data from the secondary NVM system, then switches the wireless device back to the primary NVM system once it has been restored. If the secondary NVM system has failed then the NVM manager restores the secondary NVM system using data from the primary NVM system.

Abstract: A system and method for recovering from logical path failures is set forth. More specifically, when a host detects a logical path failure, the host enters a path discovery mode of operation. If the host continues to detect a logical path failure while operating in the logical path discovery mode of operation, the host removes the logical path from a logical path mask, and the host does not use the removed logical path again. Additionally, the system and method facilitates recovery of the failed logical paths by using a plurality of logical path masks. A first mask is referred to as an intermediate failure logical path mask and a second mask is referred to as a permanent failure logical path mask.

Abstract: When data of HDD of computer is backed up to a a data center and a failure occurs in the HDD, the computer notifies failure information to the data center, and the data center stores the backed up data in a storage medium substituting HDD for subsequent delivery. Further, the computer executes processing, using a VNC server, from failure occurrence until recovery.

Abstract: A method of wear leveling in a flash storage device comprising a plurality of data blocks is provided. The method comprises the steps of detecting a data error in a read of dynamic data from a first data segment of a first data block of the plurality of data blocks, correcting the data error, and moving the dynamic data from the first data segment to a second data segment in a second one of the plurality of data blocks.

Abstract: A RAID is configured using plural nonvolatile semiconductor memory devices to enable recovery of data stored in the nonvolatile semiconductor memory devices, and data is read from the nonvolatile semiconductor memory device included in the RAID in response to a data reading request inputted from outside. When an error occurs during the reading, data for which the reading error occurs is recovered, and rewritten into an area of the nonvolatile semiconductor memory device in which the reading error occurs.

Abstract: An apparatus, system, and method for providing error protection for data-masking bits in a memory device of a memory system are provided. The memory device includes a memory core to store data, and a data interface to receive the data and data-masking bits associated with a write command. The memory device also includes a gating block to control writing the data to the memory core, where the writing of the data to the memory core is inhibited upon detecting an error with one or more of the data-masking bits.

Abstract: When data in one semiconductor memory device is corrupted during a padding process by a padding unit and the data cannot be recovered even by using an error correcting code for correcting a data error, a storage control device issues a data recovery request to a data recovery device. The data recovery device reads the data from other semiconductor memory device in response to the data recovery request to recover the data, and returns a recovery result to the padding unit in the storage control device to perform the padding process.

Abstract: A disk drive. The disk drive includes a non-volatile memory that is incapable of being overwritten more than a limited number of times, a disk and a controller. The controller includes a memory management table used to manage a correlation between a logical block address (LBA) and a physical address of the non-volatile memory. In the absence of a replaceable region in the non-volatile memory and in response to an occurrence of a failure to write data in a region, defined as a failure region, in the non-volatile memory at a first physical address correlated with a first LBA, the controller is configured to write the data at a second physical address correlated with a second LBA of the non-volatile memory different from the first LBA, and is configured to correlate in the memory management table the first LBA with the second physical address.

Abstract: A method, system and computer program product for preserving data in a storage subsystem having dual cache and dual nonvolatile storage (NVS) through a failover from a failed cluster to a surviving cluster, the surviving cluster undergoing a rebooting process, is provided. A memory preserved indicator associated with a cache of the surviving cluster is detected. The memory preserved indicator designates marked tracks having an image in an NVS of the failed cluster to be preserved through the rebooting process. A counter in a data structure of the surviving cache is incremented. If a value of the counter exceeds a predetermined value, a cache memory is initialized, and the marked tracks are removed from the cache to prevent an instance of repetitive reboots caused by a corrupted structure in the cache memory.

Abstract: The present invention presents techniques for the linking of physical blocks of a non-volatile memory into composite logical structures or “metablocks”. After determining an initial linking of good physical blocks into metablocks, a record of the linking is maintained in the non-volatile memory where it can be readily accessed when needed. In one set of embodiments, the initially linking is deterministically formed according to an algorithm and can be optimized according to the pattern of any bad blocks in the memory. As additional bad blocks arise, the linking is updated using by replacing the bad blocks in a linking with good blocks, preferably in the same sub-array of the memory as the block that they are replacing.

Abstract: A storage system encrypts plain text from an external device and stores the cryptogram into a disk unit, decrypts stored data in the disk unit and transmits decrypted text to the external device. The plain and decrypted text must be in agreement when seen from the external device. If a failure occurs in the encrypting or decrypting process, the plain and decrypted text disagree. The storage system includes an encryption unit for encrypting first data, a decryption unit for decrypting the encrypted data into second data, and a comparison unit for comparing the first and second data. When the first and second data do not agree, the first data is encrypted by a different encryption unit and the encrypted data is decrypted into third data, whereupon the first and third data are compared. When the first and third data do not agree, a failure report is sent.

Abstract: Proposed are a storage system, data processing method and storage apparatus capable of performing stable data I/O processing. Each of the storage apparatuses configured in the storage group stores group configuration information containing priority information given to each storage apparatus, and the storage apparatus with the highest priority becomes a master and performs virtualization processing and data I/O processing, and another storage apparatus belonging to this storage group performs internal processing of the storage group.

Abstract: An apparatus maintenance system and method are provided. The apparatus maintenance system includes an apparatus including a first control part, and a second control part connected to the first control part and a maintenance-data management server managing maintenance data about the apparatus. The second control part downloads the maintenance data from the maintenance-data management server to transfer the downloaded maintenance data to the first control part and transmits a maintenance result transferred from the first control part to the maintenance-data management server.

Abstract: A system and a method for causing migration of VNASs formed on NAS heads of one NAS system to other NAS heads on the same NAS system or on other NAS systems including independent storage systems. A VNAS management program on each NAS head includes a VNAS assign program, a failure detect program and a load balance program, that all include a capability for causing remote migration of VNASs on the NAS head in case a VNAS fails, the NAS head fails, or the entire NAS system fails. The VNAS management capability may cause VNAS migration if a NAS head is over loaded or if it is lightly loaded and may be powered down after its VNASs have been transferred.

Abstract: According to an aspect of an embodiment, a method for controlling a controller connected to a plurality of storage units storing data, the controller including a cache and a buffer, the method comprising the steps of: storing data in the cache; generating parity data corresponding to the data and storing the parity data in the buffer; writing the data and the parity data into the plurality of the storage units; comparing the parity data stored in the buffer with the parity data written into and read out from at least one of the storage unit; deleting, when the parity data stored in the buffer is different from the parity data read out from the storage unit, the parity data from the buffer; and regenerating parity data from data stored in the cache and rewriting the regenerated parity data into at least one of the storage unit.

Abstract: A memory system, data processing system, and method are provided for using cache that is embedded in a memory hub device to replace failed memory cells. A memory module comprises an integrated memory hub device. The memory hub device comprises an integrated memory device data interface that communicates with a set of memory devices coupled to the memory hub device and a cache integrated in the memory hub device. The memory hub device also comprises an integrated memory hub controller that controls the data that is read or written by the memory device data interface to the cache based on a determination whether one or more memory cells within the set of memory devices has failed.

Abstract: In a system management apparatus, a failure detection unit detects a readout failure in one of blocks constituting distributed data stored in a first RAID disk array. A request unit requests a computer to supplement one of the blocks of the distributed data stored in the first RAID disk array in which a readout failure irrecoverable by use of only the data stored in the first RAID disk array occurs, where the computer has a second RAID disk array storing a duplicate of the distributed data stored in the first RAID disk array. And an overwriting unit receives data corresponding to the one of the blocks from the computer, and overwrites the one of the blocks with the received data.

Abstract: A disk drive system and method capable of dynamically allocating data is provided. The disk drive system may include a RAID subsystem having a pool of storage, for example a page pool of storage that maintains a free list of RAIDs, or a matrix of disk storage blocks that maintain a null list of RAIDs, and a disk manager having at least one disk storage system controller. The RAID subsystem and disk manager dynamically allocate data across the pool of storage and a plurality of disk drives based on RAID-to-disk mapping. The RAID subsystem and disk manager determine whether additional disk drives are required, and a notification is sent if the additional disk drives are required. Dynamic data allocation and data progression allow a user to acquire a disk drive later in time when it is needed. Dynamic data allocation also allows efficient data storage of snapshots/point-in-time copies of virtual volume pool of storage, instant data replay and data instant fusion for data backup, recovery etc.

Abstract: A method for repairing a main memory comprises the steps of: utilizing a spare memory to repair a main memory, wherein the spare memory includes a plurality of spare memory units; allocating a spare memory unit; determining whether available permutations of the allocated spare memory unit cover a newly found defect in the main memory; removing permutations of the spare memory unit failing to cover newly found defects in the main memory; and allocating another spare memory unit to repair the newly found defects if available permutations of the allocated spare memory unit fails to cover the newly found defects.

Abstract: A nonvolatile memory device comprises a nonvolatile memory and a memory controller. The nonvolatile memory includes the same memory cells striding over a plurality of pages. A page information instruction part has the page structure information of the nonvolatile memory. According to this information, a related page identification part identifies a page (related page) in which the data may change. The relation data stored in the related page are temporarily stored into a save memory before an error occurs, and if an error exists, these relation data are used to repair the data that have changed. By this method, in a memory device using a nonvolatile memory including the same memory cells striding over a plurality of pages, even if an error occurs during data writing, the error is repaired and the reliability can be ensured.

Abstract: A data processing system having a plurality of hardware units providing a predetermined set of functional capabilities. The data processing system is configurable to allow selectively electronically enabling at least a subset of the functional capabilities. The system comprises a portion for receiving a replaceable hardware unit. The system also comprises a control unit for determining a type of the replaceable hardware unit. The control unit is configured to determine the subset of functional capabilities to be electronically enabled and electronically enabling the determined subset of functional capabilities if the replaceable hardware unit is of a first type. The control unit is also configured to enable entire functional capabilities of the replaceable hardware unit if the replaceable hardware unit is of a second type.

Abstract: There is provided a test apparatus including a plurality of test signal feeding sections that are provided in a one-to-one correspondence with the plurality of memories under test, where each of the plurality of test signal feeding sections feeds a test signal designed to test a corresponding one of the plurality of memories under test to the corresponding memory under test, a plurality of defect detecting sections that are provided in a one-to-one correspondence with the plurality of memories under test, where each of the plurality of defect detecting sections detects a defect in a corresponding one of the plurality of memories under test, a plurality of first calculating sections that are provided in a one-to-one correspondence with the plurality of memories under test, where each of the plurality of first calculating sections calculates a remedy solution for a corresponding one of the plurality of memories under test and the remedy solution remedies the defect in the corresponding memory under test by repl

Abstract: A method and system for a non-volatile memory (NVM) with multiple bits error correction are provided and may include detecting bit errors in a memory element, of a NVM array integrated within a chip, which remain uncorrected after forward error correction. A redundant memory element may be utilized when the errors may be detected utilizing a cyclic redundancy check, may be within the NVM array, and may include secure information. Access to the secure information and/or the chip may be disabled when the errors are detected. The FEC operation may include one or both of an error location operation and a correction operation. The errors may be corrected when a location may be known to include the errors. The NVM array may be partitioned into regions. At least one of the redundant memory elements may be substituted in place of the memory element based on a substitution priority.

Abstract: In one or more of the disclosed embodiments, memory cells in a memory device are refreshed upon an indication of a fatigue condition. In one such embodiment, controller monitors behavior parameters of the cells and determines if any of the parameters are outside of a normal range set for each one, thus indicating a fatigue condition. If any cell indicates a fatigue condition, the data from the block of cells indicating the fatigue is moved to another block. In one embodiment, an error detection and correction process is performed on the data prior to being written into another memory block.

Abstract: Memory apparatus and methods utilizing multiple bit lanes may redirect one or more signals on the bit lanes. A memory agent may include a redrive circuit having a plurality of bit lanes, a memory device or interface, and a fail-over circuit coupled between the plurality of bit lanes and the memory device or interface.

Abstract: A cluster recovery process is implemented across a set of distributed archives, where each individual archive is a storage cluster of preferably symmetric nodes. Each node of a cluster typically executes an instance of an application that provides object-based storage of fixed content data and associated metadata. According to the storage method, an association or “link” between a first cluster and a second cluster is first established to facilitate replication. The first cluster is sometimes referred to as a “primary” whereas the “second” cluster is sometimes referred to as a “replica.” Once the link is made, the first cluster's fixed content data and metadata are then replicated from the first cluster to the second cluster, preferably in a continuous manner. Upon a failure of the first cluster, however, a failover operation occurs, and clients of the first cluster are redirected to the second cluster.

Abstract: A management server obtains configuration information of an active server and creates a logical partition in a backup server so as to correspond to the active server. The backup server starts up the created logical partition. And when the created logical partition reaches a predetermined state, the backup server releases allocation of the first processor resource to the logical partition, thereby the logical partition stands by. The management server, when detecting an error occurred in the active server, stops the active server and searches the logical partition having same configuration as the active server in which error is detected, and enables allocation of the first processor resource to the searched logical partition, thereby completing the start-up of the logical partition.

Abstract: Spare disk drives are provided to a chassis for storing storage devices, and, when any one of the storage devices configuring RAID fails, the storage controller copies data of the failed storage device to a spare storage device, and recognizes an additional storage device inserted into the spare disk drive as the spare storage device. Thereafter, when the foregoing storage device fails, the storage controller reproduces data of the failed storage device, copies this data to an additional storage device inserted into the spare disk drive, and recognizes the additional storage device inserted into the spare disk drive as a spare storage device. Subsequently, when the foregoing storage device fails, the storage controller reproduces data of the failed storage device and copies this data to an additional storage device inserted into the spare disk drive. RAID 6 is maintained thereby.