Abstract: One aspect of the present invention provides a system for failover comprising at least one client selectively connectable to one of at least two interconnected servers via a network connection. In a normal state, one of the servers is designated a primary server when connected to the client and a remainder of the servers are designated as backup servers when not connected to the client. The at least one client is configured to send messages to the primary server. The servers are configured to process the messages using at least one service that is identical in each of the servers. The services are unaware of whether a server respective to the service is operating as the primary server or the backup server. The servers are further configured to maintain a library, or the like, that indicates whether a server is the primary server or a server is the backup server. The services within each server are to make external calls via its respective library.

Abstract: A data storage system includes a first storage processor including a first memory device; a second storage processor including a second memory device; and a third memory device coupled to the first storage processor and the second storage processor. The first and second storage processors are interconnected to enable mirroring of data between the first memory device and the second memory device. During a first mode of operation, data processed by the first storage processor and the second storage processor is mirrored between the first memory device and the second memory device and, during a second mode of operation, data processed by the first storage processor is mirrored from the first memory device to the third memory device.

Abstract: A method for operating a mirrored disk storage system, comprises a detector component operable to detect that a failure has left read stability in doubt, a determiner component for determining a repair characteristic of a pair of mirrored disks, a comparator for comparing the repair characteristic of a first of the pair with the repair characteristic of a second of the pair, and a selector for selecting one of the first or the second of the pair having a preferred repair characteristic to be used as a synchronization source disk. The preferred repair characteristic comprises the characteristic that no repair is required for the one of the first or the second of the pair, or that a least repair time is required for the one of the first or the second of the pair.

Abstract: A storage controller detects a failure of any one of storage units making up a RAID group. The storage controller incorporates plural hot spares HS into the RAID group, as substitute storage units for the detected failed storage. The storage controller restores the memory contents of the failed storage unit onto each of the hot spares incorporated into the RAID group. Upon detecting replacement of the failed storage unit in the RAID group, the storage controller incorporates into the RAID group, a replacement storage unit that has replaced the failed storage unit.

Abstract: A system is provided. The system detects a dropped write from a hard disk drive (HDD). The system includes two or more HDDs, each being configured to define a data block spread across the two or more HDDs. The data block is configured to regenerate a checksum across the full data block during a read operation to detect the dropped write.

Abstract: Performing data management operations on replicated data in a computer network. Log entries are generated for data management operations of an application executing on a source system. Consistency point entries are used to indicate a time of a known good, or recoverable, state of the application. A destination system is configured to process a copy of the log and consistency point entries to replicate data in a replication volume, the replicated data being a copy of the application data on the source system. When the replicated data represents a known good state of the application, as determined by the consistency point entries, the destination system(s) may perform a storage operation (e.g., snapshot, backup) to copy the replicated data and to logically associate the copied data with a time information (e.g., time stamp) indicative of the source system time when the application was in the known good state.

Abstract: A distributed storage integrity system in a dispersed storage network includes a scanning agent and a control unit. The scanning agent identifies an encoded data slice that requires rebuilding, wherein the encoded data slice is one of a plurality of encoded data slices generated from a data segment using an error encoding dispersal function. The control unit retrieves at least a number T of encoded data slices needed to reconstruct the data segment based on the error encoding dispersal function. The control unit is operable to reconstruct the data segment from at least the number T of the encoded data slices and generate a rebuilt encoded data slice from the reconstructed data segment. The scanning agent is located in a storage unit and the control unit is located in the storage unit or in a storage integrity processing unit, a dispersed storage processing unit or a dispersed storage managing unit.

Abstract: Embodiments of the invention relate to data replication and block allocation in a file system to support write transactions. Regions in a cluster file system are defined to support a block allocation. Blocks in the defined regions are allocated to support the data replication. A pipeline manager is provided to schedule population of the blocks in the allocated region(s) based upon network characteristics.

Abstract: A size comparison unit reports, to an access control unit, the size of a piece of compressed data having the smallest size from among pieces of compressed data generated via compression processing units compressing blocks, an algorithm name representing a compression processing unit that has generated the piece of compressed data having the smallest size; the access control unit selects a piece of compressed data to be written in a tape medium and reports, to a statistical information processing unit, an algorithm name representing a compression processing unit that has generated this selected piece of compressed data; the statistical information processing unit extracts, from the reported algorithm name, a regularity present in a result of the selection of compressed data and, in accordance with this extracted regularity, specifies and stops a compression processing unit to be stopped.

Abstract: A duplicate-aware disk array (DADA) leaves duplicated content on the disk array largely unmodified, instead of removing duplicated content, and then uses these duplicates to improve system performance, reliability, and availability of the disk array. Several implementations disclosed herein are directed to the selection of one duplicate from among a plurality of duplicates to act as the proxy for the other duplicates found in the disk array. Certain implementations disclosed herein are directed to scrubbing latent sector errors (LSEs) on duplicate-aware disk arrays. Other implementations are directed to disk reconstruction/recovery on duplicate-aware disk arrays. Yet other implementations are directed to load balancing on duplicate-aware disk arrays.

Abstract: Embodiments of the invention relate to data replication and block allocation in a file system to support write transactions. Regions in a cluster file system are defined to support a block allocation. Blocks in the defined regions are allocated to support the data replication. A pipeline manager is provided to schedule population of the blocks in the allocated region(s) based upon network characteristics.

Abstract: A non-volatile memory device includes first and second memory regions to store data and a memory control unit. Each of the first and second memory regions is configured by a plurality of physical pages. Each of the physical pages is configured by a plurality of regions corresponding to a plurality of logical addresses. The memory control unit performs control of batch erasing and batch writing on every physical page. When a first physical page in the first memory region includes a first region corresponding to a first logical address, which is a target to be written, and when a second physical page in the second memory region includes a second region corresponding to the first logical address, which is a target to be written, the memory control unit selects either the first physical page or the second physical page as a physical page for writing.

Abstract: A method, device, and computer readable medium for striping rows of data across logical units of storage with an affinity for columns is provided. Alternately, a method, device, and computer readable medium for striping columns of data across logical units of storage with an affinity for rows is provided. When data of a logical slice is requested, a mapping may provide information for determining which logical unit is likely to store the logical slice. In one embodiment, data is retrieved from logical units that are predicted to store the logical slice. In another embodiment, data is retrieved from several logical units, and the data not mapped to the logical unit is removed from the retrieved data.

Abstract: In a memory with block management system, program failure in a block during a time-critical memory operation is handled by continuing the programming operation in a breakout block. Later, at a less critical time, the data recorded in the failed block prior to the interruption is transferred to another block, which could also be the breakout block. The failed block can then be discarded. In this way, when a defective block is encountered during programming, it can be handled without loss of data and without exceeding a specified time limit by having to transfer the stored data in the defective block on the spot. This error handling is especially critical for a garbage collection operation so that the entire operation need not be repeated on a fresh block during a critical time. Subsequently, at an opportune time, the data from the defective block can be salvaged by relocation to another block.

Abstract: A high availability DAS system uses a solid state cache to provide near active-active performance in a DAS duster, while retaining the implementation simplicity of active-passive or dual active system. Each node in the duster may include a solid state cache that stores hot I/O in an active-active mode, which allows the data to be read from or written to the underlying dual-active or active/passive DAS RAID system only when access to the “hot Region” cools down or in the case of Cache Miss. The hot I/O data includes hot read data that accumulated dynamically regardless of ownership of the drives where the hot read data is permanently stored. The hot I/O data also includes hot write data that is mirrored across the solid state cache memories to avoid potential dirty write data conflicts and also to provide High Availability in case of server failures.

Abstract: A system, computer program product, and computer-implemented method for defining a data stripe that spans one or more of N data storage devices and one or more of M erasure code devices. The one or more N data storage devices and the one or more M erasure code devices are included within a data storage system. A data chunk to be written to the data storage system is received. At least a portion of the data chunk is written to the portion of the data stripe that spans the one or more N data storage devices. Each of the N data storage devices and the M erasure code devices is included within a unique server computer.

Abstract: In one embodiment, an apparatus includes memory comprising a first portion in which data contained therein is mirrored and a second portion wherein data contained therein is not mirrored, a memory allocator for allocating the first portion of the memory to critical data and allocating the second portion of the memory to non-critical data, and a processor for mirroring the critical data and receiving an indication of a memory error. If the memory error occurs in the first portion of the memory, a mirrored copy of the critical data is used. If the memory error occurs in the second portion of the memory, the memory error is contained so that the apparatus can continue to operate programs using the memory not affected by the memory error.

Abstract: Replicated instances in a database environment provide for automatic failover and recovery. A monitoring component can periodically communicate with a primary and a secondary replica for an instance, with each capable of residing in a separate data zone or geographic location to provide a level of reliability and availability. A database running on the primary instance can have information synchronously replicated to the secondary replica at a block level, such that the primary and secondary replicas are in sync. In the event that the monitoring component is not able to communicate with one of the replicas, the monitoring component can attempt to determine whether those replicas can communicate with each other, as well as whether the replicas have the same data generation version. Depending on the state information, the monitoring component can automatically perform a recovery operation, such as to failover to the secondary replica or perform secondary replica recovery.

Abstract: A system comprises at least two random access memory (RAM) elements arranged to store data redundantly. The system further comprises RAM routing logic comprising comparison logic operably coupled to the at least two RAM elements and arranged to compare redundant data read from the at least two RAM elements, and check and validation logic, independent of the RAM routing logic, operably coupled to the at least two RAM elements and arranged to additionally detect an error in the redundant data read from the at least two RAM elements and provide an error indication signal to the RAM routing logic in response thereto. The RAM routing logic further comprises selection logic arranged to dynamically select redundant data from one of the at least two RAM elements based on the comparison of the redundant data and the error indication signal.

Abstract: An electronic money system includes a plurality of electronic money terminals for withdrawing a sum of money which is spent by a user from money data which has been deposited into an information card. Utilization-history data including the number of times the information card has been utilized, and accumulated in the information card is read out at the time when data relating to the spent money is also withdrawn from the information card. Utilization-history data read out from each of the electronic money terminals are gathered and coordinated, so as to coordinate and tabulate the utilization-histories of the information card which has been utilized on any of the plurality electronic money terminals.

Abstract: Since the whole storage device is blocked according to the conventional data saving method when failure occurs to the storage device in a storage subsystem, so that when failure occurs to two storage devices at the same time within a same RAID group, double failure is caused and data loss occurs. In order to solve the problem, the present invention divides a storage device into storage areas of predetermined units, constructs RAID groups from two or more storage areas, and when failure occurs to the storage area, selects a data migration destination storage area from either the RAID group in which failure has occurred or the RAID group other than the RAID group in which failure has occurred, migrates the data stored in the storage area where failure has occurred to the selected data migration destination storage area, and blocks only the storage area where failure has occurred.

Abstract: A method for storing data. The method includes receiving a request to write data, determining that the storage mode for the data is mirrored mode, selecting a Redundant Array of Independent Devices (RAID) grid location in a RAID grid to write the data based on the storage mode, writing the data to memory, updating a data structure to indicate that the RAID grid location is filled, and determining a data grid is filled. Based on the determination, determining a first physical address and a second physical address in persistent storage corresponding to the RAID grid location; writing the data to a first physical location in the persistent storage corresponding to the first physical address and writing the data to a second physical location in the persistent storage corresponding to the second physical address, and writing the parity values associated with data grid to the persistent storage.

Abstract: In one embodiment, the present invention includes a method for receiving an indication of a loss of redundancy with respect to a pair of mirrored memory regions of a partially redundant memory system, determining new mirrored memory regions, and dynamically migrating information stored in the original mirrored memory regions to the new mirrored memory regions. Other embodiments are described and claimed.

Abstract: Systems and methods for fault handling are presented. In one embodiment, a fault handling method includes: performing an error type detection process including determining if an error is a media error or a connectivity error; performing a detachment determination process to establish an appropriate detachment scenario, wherein the appropriate detachment scenario includes not detaching any mirrors if the connectivity error involves all mirrors; and returning an application write with a failure. In one embodiment, the detachment determination process detaches a mirror in accordance with results of a read-write-back process. In one exemplary implementation, the detachment determination process includes a connectivity status inquiry and mirrors are detached in accordance with results of the connectivity status inquiry. In one exemplary implementation, the connectivity status inquiry includes a SCSI connectivity inquiry.

Abstract: A deduplication storage capacity is estimated as a function of an expected deduplication ratio, the expected deduplication ratio being a combined average of a current deduplication ratio and a configured deduplication ratio, the current deduplication ratio depending on the data currently stored in the deduplication storage, and the configured deduplication ratio being an estimate made at a configuration stage of the deduplication computing storage environment.

Abstract: A first controller defines an existing pair that represents a copy from a first existing area that is a storage area of a first logical volume before size expansion to a second existing area that is a storage area of a second logical volume before size expansion, maintains the existing pair in a synchronous state, which is a state where the second existing area is in synchronization with the first existing area, and expands the size of the first logical volume by adding a first expansion area using a first storage device to the first logical volume during the synchronous state, and the second controller adds a second expansion area using a second storage device to the second logical volume after the size of the first logical volume is expanded, and writes data written to the first expansion area to the second expansion area.

Abstract: A data protection method for damaged memory cells is provided. A power-on self-test (POST) is executed, and an initial backup memory is reserved in a memory. An operating system (OS) is executed, and data is loaded from a kernel region of the OS in the memory into a mirror region, so that when a processor accesses the data in the kernel region, it also accesses the data in the mirror region. An uncorrectable error (UE) is detected to determine a damaged page, and a backup page is selected from the initial backup memory or dynamically obtained from the OS to back up data in the damaged page. A mapping address of the damaged page and backup page are recorded into a page mapping table in a memory controller. Accordingly, when the OS accesses the damaged page, the memory controller accesses the backup page instead according to the page mapping table.

Abstract: The present disclosure is a system and method for improved RAID rebuilds under host IO conditions, that greatly improves rebuild times and prevents host IO starvation. A queue in a drive that is part of the RAID is used to store rebuild and host IO requests, with rebuild IOs issued to the head of the drive queue. Rebuild requests in the drive are delayed by a delay time. This delay ensures there is no unintended side effect of this invention that may result in host IO starvation for the RAID system. Delay is computed as a heuristic function from a plurality of variables, such as disk head response times, time allotted for rebuild, number of rebuild threads, drive behavior, rebuild IO profile, host IO profile including workload and locality, and a timeline of sequenced events, which in one preferred embodiment cycles every 70 seconds.

Abstract: Various embodiments for reducing communication between cluster nodes and optimizing failover processing in a distributed shared memory (DSM)-based application by at least one processor device are provided. In one embodiment, for a data structure operable on a DSM, a read-mostly portion is maintained in a single copy sharable between the cluster nodes while an updatable portion is maintained in multiple copies, each of the multiple copies dedicated to a single cluster node.

Abstract: A redundant array of independent disks level 5 (RAID 5) with a mirroring functionality is disclosed. In one embodiment, a method for adding a mirroring functionality to a RAID 5 includes forming an array using at least three drives for storing data, creating multiple data blocks and a parity for the multiple data blocks based on the data for every (2N?1)th stripe of the array, and generating a mirror image of the multiple data blocks and the parity for the multiple data blocks for every (2N?1)th stripe to its respective 2Nth stripe of the array, where the N is an integer starting from 1.

Abstract: A method, system, apparatus, and computer-readable medium are described for providing distributed hot-spare storage in a redundant storage cluster. According to one method, a portion of the unutilized space on the storage cluster is utilized as a distributed hot-spare storage node. Through this mechanism, a redundant storage cluster with N storage nodes may be contracted to a redundant array with N?1 nodes. Thin provisioning and intelligent data placement may also be utilized to implement the distributed hot-spare storage node. Through repeated application of such methods and systems, the failure of any storage node or the sequential failure of multiple storage nodes within a redundant storage cluster results in the recreation of the cluster as a redundant storage array with one fewer node, but with the same redundancy.

Abstract: A method for data storage includes encoding data with an inter-device Error Correction Code (ECC), and sending the encoded data for storage on two or more storage devices. The data to be stored on each of the storage devices, and which has been encoded with the inter-device ECC, is encoded with an intra-device ECC, and the data encoded with the inter-device and intra-device ECCs is stored on the storage device. After storing the data, at least part of the stored data is retrieved and output by decoding the intra-device and inter-device ECCs, while using information related to one of the intra-device and inter-device ECCs in decoding the other of the intra-device and inter-device ECCs.

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: A computer-readable medium storing a data management program makes a computer manage data redundantly stored in storage devices having storage areas split into slices for data management. The data management program realizes the following functions in the computer. A first function receives irregularity information indicating that each of one or more of the storage devices may be possibly faulty, and stores the irregularity information in a storage; and a second function determines, by reference to the irregularity information, whether or not a first storage device containing a slice to be accessed is possibly faulty, on receipt of access information indicating occurrence of a request to access the slice. When yes is determined, the second function instructs an external device to recover data stored in the slice, where the external device controls a second storage device storing redundant data identical to the data stored in the slice.

Abstract: Data written in the primary logical volume of the first storage device are transmitted to the third storage device via the second storage device, the data being written in the same location as the primary logical volume within the secondary logical volume in the third storage device; when transmission of the data stops among the first to the third storage devices, the respective second storage device and the third storage device manage locations in the secondary logical volume where the data held thereby are to be written; and, when transmission of the data resumes among the first to the third storage devices, the locations in the secondary logical volume managed by the respective second and the third storage devices are aggregated, the data to be written in the respective aggregated location in the secondary logical volume being transmitted from the first storage device to the third storage device via the second storage device.

Abstract: A computer executes a data allocation control program to control allocation of data in a plurality of disk nodes. A redundancy restoration module executes a redundancy restoration procedure by commanding disk nodes to create a new copy of redundancy-lost data. An error message reception module receives a write error message indicating a write error in a storage device during the redundancy restoration procedure and records an identifier of the faulty storage device in an error record memory. A copy command module identifies accessed data in the faulty storage device and commands a relevant disk node to create a copy of the identified data in the faulty storage device in the case where there is no redundant copy of the data.

Abstract: Multiple copy sets of data are maintained on one or more storage devices. Each copy set includes at least some of the same data units as other sets. Different sets optionally have data units stored in different orders on the storage device(s). A particular one of the sets of data is selected as the set to be accessed in response to detecting a particular scenario.

Abstract: In a storage system which supports a redundant disk configuration, while securing fault tolerance, a longer drive access time as well as a drop in I/O throughput are prevented when a redundant data update, generated due to a data update, is mirrored in the drive. A controller for controlling data I/O to and from the drive updates first redundant data and block data of a corresponding data stripe in the disk drive in correspondence with an update of block data of the logical volume, and the controller updates second redundant data on the basis of a predetermined number of block data which belong to the same data stripe as the updated block data with different timing from the update of the block data.

Abstract: A system, program product, and computer implemented method for data replication, comprising enabling a virtual service layer to consume a storage medium of a site and map the storage medium of the site as one or more virtual storage volumes, enabling the virtual service layer to present the one or more virtual storage volumes for consumption by a host, enabling a splitter of the site to intercept I/O written to the one or more virtual storage volumes, splitting intercepted I/O to a journal based replication appliance, and enabling the journal based replication appliance to create a continuous data protection image of the data written to one or more virtual storage volumes.

Abstract: A storage system, method and program product, the system comprising: storage devices; and a controller configured to: provide virtual volumes to a host computer; manage logical units on the storage device and storage pools; allocate, in response to receiving a write request to a virtual volume, a storage region of the storage pools; and store data related to the write request in the storage region allocated, wherein the controller is further configured to: allocate first storage region in first storage pool to first virtual volume based on first size of the first storage region or the first virtual volume; allocate a second storage region in a second storage pool to a second virtual volume of the plurality of virtual volumes based on a second size of the second storage region or the second virtual volume.

Abstract: A system and method of creating an extra redundancy in a RAID system is disclosed. In one embodiment, one or more RAID arrays are created. Each RAID array comprises a plurality of disk drives. Further, a respective dedicated hot spare is created for each RAID array. Furthermore, data is copied from each RAID array to the respective dedicated hot spare using a copyback process based on a predetermined controller usage threshold value.

Abstract: A method, apparatus, article of manufacture, and system are presented for establishing redundant computer resources. According to one embodiment, in a system including a plurality of processor devices and a plurality of storage devices, the processor devices, the storage devices and the management server being connected via a network, the method comprises storing device information relating to the processor devices and the storage devices and topology information relating to topology of the network, identifying at least one primary computer resource, selecting at least one secondary computer resource suitable to serve as a redundant resource corresponding to the at least one primary computer resource based on the device information and the topology information, and assigning the at least one secondary computer resource as a redundant resource corresponding to the at least one primary computer resource.

Abstract: In one embodiment, the present invention provides an ability to handle an error occurring during a memory migration operation in a high availability system. In addition, a method can be used to dynamically remap a memory page stored in a non-mirrored memory region of memory to a mirrored memory region. This dynamic remapping may be responsive to a determination that the memory page has been accessed more than a threshold number of times, indicating a criticality of information on the page. Other embodiments are described and claimed.

Abstract: A method and apparatus for transparently handling recurring correctable errors and uncorrectable errors in a mirrored memory system prevents costly system shutdowns for correctable memory errors or system failures from uncorrectable memory errors. When a high number of correctable errors are detected for a given memory location, a memory relocation mechanism in the hypervisor moves the data associated with the memory location to an alternate physical memory location transparently to the partition such that the partition has no knowledge that the physical memory actualizing the memory location has been changed. When a correctable error occurs, the memory relocation mechanism uses data from a partner mirrored memory block as a data source for the memory block with the uncorrectable error and then relocates the data to a newly allocated memory block to replace the memory block with the uncorrectable error.

Abstract: An information handling system includes a peripheral component interconnect express root complex, a basic input output system, and a root complex mirroring block. The peripheral component interconnect express root complex includes a plurality of peripheral component interconnect express ports. The basic input output system is in communication with the peripheral component interconnect express root complex, and is configured to detect a peripheral component interconnect express adaptor configuration, and to set a peripheral component interconnect express mirroring setting based on the peripheral component interconnect express adaptor configuration. The root complex mirroring block is in communication with the basic input output system, and is configured to mirror data between a first peripheral component interconnect express adaptor and a second peripheral component interconnect express adaptor based on the peripheral component interconnect express mirroring setting.

Abstract: A spilt backup agent model where a component on a host and a component on the block storage device function together logically to provide a backup agent. In certain embodiments, the mechanism provides a split backup agent model using a NDMP protocol. The NDMP protocol is an industry standard protocol that allows for backup of hosts with a single backup agent that is compatible with multiple independent software vendor (ISV) backup software. Thus with the present invention, proprietary backup software dependent host agents are not required. The NDMP protocol provides for separation of control and data connections where the control path runs between the data server on the host that needs to be backed up and backup software (e.g., a Data Management Application (DMA)) and between the backup device and the backup software. The data path runs between the host and the backup device.

Abstract: A computer-implemented method for improving redundant storage fault tolerance may include 1) identifying a plurality of storage devices storing an encoded set of data, with the encoded set of data including a redundant form of an underlying set of data, 2) determining that a subset of the plurality of storage devices have failed, 3) reconstructing encoded data lost due to the failure of the subset of the plurality of storage devices, and then 4) redundantly storing the reconstructed encoded data on the plurality of storage devices. Various other methods, systems, and computer-readable media are also disclosed.

Abstract: Described herein is a high-availability storage system having hierarchical levels of storage functions. The storage system may comprise one or more hierarchical levels, each hierarchical level comprising physical servers and be assigned to perform a particular set of storage functions. Each physical server may implement one or more VMs configured to perform only the set of storage functions assigned to the hierarchical level on which the VM executes. VMs of a first hierarchical level may be configured to organize the VMs of a second hierarchical level into a redundant array of storage access servers for providing data reliability and high-availability of the storage system. VMs of a first hierarchical level are configured to produce and route sub-requests to the VMs of a second hierarchical level. Failure of a sub-request is detected and remedied by a VM of the first hierarchical level.

Abstract: A data center system includes a memory cache coupled to a data center controller. The memory cache includes volatile memory and stores data that is persisted in a database in a different data center system that is located remotely from the data center system rather than in the first data center system. The data center controller reads data from the memory cache and writes data to the memory cache.

Abstract: This invention provides a user or an operator with a management apparatus or method for displaying logical connection information between an interface connected to a computer and a switch and a storage system or a logical unit in the storage system in a virtual storage system, wherein the switch receives a first access request from said computer, converts said first access request to a second access request to one of said plural storage systems, and sends said second access request to one of said plural storage systems or one logical unit.