Abstract: A data storage system is provided with a pair of controllers and circuitry configured for failing back from a single active write back mode to a dual active write back mode by copying cached data directly from a cache of a survivor controller of the pair of controllers to a cache of the other controller. A method is provided for failing over from a dual active mode of first and second controllers to a single active mode of the first controller by relying on previously mirrored cache data by the second controller; reinitializing the second controller; and failing back to the dual active mode by copying cached data directly from the first controller to the second controller.

Abstract: A very large virtual volume (e.g., in excess of 500 GB) is formed by distributing the disks in eleven, six-disk RAID-5 sets across the six busses of a primary local back-end controller. A spare disk is provided on each of the six busses. Each RAID-5 set is protected from the failure of a single disk by the spare disks on the busses, which can use the parity data stored in a RAID-5 set to rebuild the data stored on a failing disk and thereby restore redundancy to the RAID-5 set. Each RAID-5 set is also protected from the failure of a bus by the parity inherent in RAID-5. The RAID-5 sets are striped by a front-end controller connected to the primary local back-end controller, and the striped RAID-5 sets are presented to a host computer as a very large virtual volume. If the individual disks are 9.1 GB in size, the size of the very large virtual volume can reach 500.5 GB.

Abstract: A data storage system is provided with a pair of controllers and circuitry configured for failing back from a single active write back mode to a dual active write back mode by copying cached data directly from a cache of a survivor controller of the pair of controllers to a cache of the other controller. A method is provided for failing over from a dual active mode of first and second controllers to a single active mode of the first controller by relying on previously mirrored cache data by the second controller; reinitializing the second controller; and failing back to the dual active mode by copying cached data directly from the first controller to the second controller.

Abstract: A disaster-tolerant data backup and remote copy system which is implemented as a controller-based replication of one or more LUNs (logical units) between two remotely separated pairs of array controllers connected by redundant links. In the situation wherein an array controller fails during an asynchronous copy operation, the partner array controller uses a ‘micro log’ stored in mirrored cache memory to recover transactions, in order, which were ‘missed’ by the backup storage array when the array controller failure occurred.

Abstract: A data replication system having a redundant configuration including dual Fiber Channel fabric links interconnecting each of the components of two data storage sites, wherein each site comprises a host computer and associated data storage array, with redundant array controllers and adapters. The system employs the grouping of logical units into ‘association sets’, for logging and failover purposes. The concept of association sets allows the system provides for proper ordering of I/O operations during logging across multiple volumes. In addition, association sets are employed by system to provide failure consistency by causing the group of logical units/volumes to all fail at the same time, ensuring a point in time consistency on the remote site.

Abstract: A very large virtual storage volume formed by distributing disks in multiple, multi-disk RAID (redundant array of independent disks) sets across busses of a back-end controller. The multiple RAID sets are striped by a front-end controller connected to the back-end controller and presented to a host computer as a very large virtual storage volume.

Abstract: A disaster-tolerant data backup and remote copy system which is implemented as a controller-based replication of one or more LUNs (logical units) between two remotely separated pairs of array controllers connected by redundant links. The system provides a method for allowing a large number of commands to be ‘outstanding’ in transit between local and remote sites while ensuring the proper ordering of commands on remote media during asynchronous or synchronous data replication. In addition, the system provides a mechanism for automatic ‘tuning’ of links based on the distance between the array controllers.

Abstract: A data replication system having a redundant configuration including dual Fibre Channel fabric links interconnecting each of the components of two data storage sites, wherein each site comprises a host computer and associated data storage array, with redundant array controllers and adapters. The system employs the grouping of logical units into ‘association sets’, for logging and failover purposes. The concept of association sets allows the system provides for proper ordering of I/O operations during logging across multiple volumes. In addition, association sets are employed by system to provide failure consistency by causing the group of logical units/volumes to all fail at the same time, ensuring a point in time consistency on the remote site.

Abstract: A disaster-tolerant data backup and remote copy system which is implemented as a controller-based replication of one or more LUNs (logical units) between two remotely separated pairs of array controllers connected by redundant links. The system provides a method for allowing a large number of commands to be ‘outstanding’ in transit between local and remote sites while ensuring the proper ordering of commands on remote media during asynchronous or synchronous data replication. In addition, the system provides a mechanism for automatic ‘tuning’ of links based on the distance between the array controllers.

Abstract: A system which provides a completely redundant configuration including dual Fibre Channel fabric links interconnecting each of the components of two data storage sites, wherein each site comprises a host computer and associated data storage array, with redundant array controllers and adapters. The array controllers perform a command and data logging function which stores all host write commands and data ‘missed’ by the backup storage array during a situation wherein the links between the sites are down, the remote site is down, or where a site failover to the remote site has occurred. Log units are used to store, in order, all commands and data for every transaction which was ‘missed’ by the backup storage array when one of the above system error conditions has occurred.

Abstract: A disaster-tolerant data backup and remote copy system which is implemented as a controller-based replication of one or more LUNs (logical units) between two remotely separated pairs of array controllers connected by redundant links. The system provides a method for allowing a large number of commands to be ‘outstanding’ in transit between local and remote sites while ensuring the proper ordering of commands on remote media during asynchronous or synchronous data replication. In addition, the system provides a mechanism for automatic ‘tuning’ of links based on the distance between the array controllers.

Abstract: A data replication system having a redundant configuration including dual Fiber Channel fabric links interconnecting each of the components of two data storage sites, wherein each site comprises a host computer and associated data storage array, with redundant array controllers and adapters. The system includes the capability of simultaneous bi-directional remote data replication which permits the system to operate in an ‘extended cluster’ mode, as if each of the remote storage arrays were local relative to the respective remote host. The system further includes the concept of ‘home’ and ‘alternate’ storage nodes, which provide for automatic node failover from a primary to a designated alternate node, without necessitating re-booting of the remote node. Write data transfers are potentially host retry-able at both sites; upon failure of controllers at one site, the host re-issues the same write on other site.

Abstract: A data replication system having a redundant configuration including dual Fiber Channel fabric links interconnecting each of the components of two data storage sites, wherein each site comprises a host computer and associated data storage array, with redundant array controllers and adapters. The system employs the grouping of logical units into ‘association sets’, for logging and failover purposes. The concept of association sets allows the system provides for proper ordering of I/O operations during logging across multiple volumes. In addition, association sets are employed by system to provide failure consistency by causing the group of logical units/volumes to all fail at the same time, ensuring a point in time consistency on the remote site.

Abstract: A data replication system having a redundant configuration including dual Fibre Channel fabric links interconnecting each of the components of two data storage sites, wherein each site comprises a host computer and associated data storage array, with redundant array controllers and adapters. Each array controller in the system is capable of performing all of the data replication functions, and each host ‘sees’ remote data as if it were local. Each array controller has a dedicated link via a fabric to a partner on the remote side of the long-distance link between fabric elements. Each dedicated link does not appear to any host as an available link to them for data access; however, it is visible to the partner array controllers involved in data replication operations. These links are managed by each partner array controller as if being ‘clustered’ with a reliable data link between them.

Abstract: A warmswap operation to replace modules in a mirrored cache system has been accomplished by disabling mirrored write operations in the cache system; testing the replacement memory module in the cache system; and restoring the mirrored data in the cache system. The restoring operation is accomplished by first quiescing write operations to stop writing data in the cache system not backed up in non-volatile data storage. Then data is copied from surviving memory modules to the replacement module, and the cooperative interaction of the surviving memory modules with the replacement memory module is validated. The validating operation verifies the cache modules are ready and the controllers are synchronized. After validation the quiesced write operations are un-quiesced, and mirrored-write operations for the cache system are enabled.

Abstract: A very large virtual volume (e.g., in excess of 500 GB) is formed by distributing the disks in eleven, six-disk RAID-5 sets across the six busses of a primary local back-end controller. A spare disk is provided on each of the six busses. Each RAID-5 set is protected from the failure of a single disk by the spare disks on the busses, which can use the parity data stored in a RAID-5 set to rebuild the data stored on a failing disk and thereby restore redundancy to the RAID-5 set. Each RAID-5 set is also protected from the failure of a bus by the parity inherent in RAID-5. The RAID-5 sets are striped by a front-end controller connected to the primary local back-end controller, and the striped RAID-5 sets are presented to a host computer as a very large virtual volume. If the individual disks are 9.1 GB in size, the size of the very large virtual volume can reach 500.5 GB.

Abstract: An apparatus and method for synchronizing a cache mode in a cache memory system in a computer to protect cache operations. The cache memory system has a first controller and a second controller and two cache modules and operates in a plurality of cache modes. The cache mode is stored as metadata in the cache modules and is detected by the first controller to determine the cache mode. Lock signals in the first controller are set in accordance with the cache mode detected to set the cache mode state in the first controller. The second controller copies the cache mode state from the first controller to synchronize both controllers in the same cache mode state. After a failure of the second controller, the first controller may lock access to both caches to recover data previously accessed by the second controller. The second controller restarts and copies the cache mode state from the first controller, so that both controllers return to the cache mode state prior to the failure of the second controller.

Abstract: A cache memory system is enabled into one of a plurality of cache modes in a cache memory system in a computer. The cache memory system has a first controller and two cache memories, the cache memories are partitioned into quadrants with two quadrants in each cache memory. A cache mode detector in the first controller detects a mirror cache mode set for the cache memory system. An address enabler in the first controller enables access to first pair of quadrants, one quadrant in each cache memory, in response to detection of a mirror cache mode. A second controller follows the cache mode set by the cache mode detector and has an address enabler. The address enabler in the second controller enables access to both quadrants in one cache memory in a non-mirror cache mode, and enables the access to a second pair of quadrants, one quadrant in each cache memory, in response to detection of a mirror cache mode by said cache mode detector.

Abstract: Disclosed is a method and apparatus for reconstructing data in a computer system employing a modified RAID 5 data protection scheme. The computer system includes a write back cache composed of non-volatile memory for storing (1) writes outstanding to a device and associated data read, and (2) storing metadata information in the non-volatile memory. The metadata includes a first field containing the logical block number or address (LBN or LBA) of the data, a second field containing the device ID, and a third field containing the block status. From the metadata information it is determined where the write was intended when the crash occurred. An examination is made to determine whether parity is consistent across the slice, and if not, the data in the non-volatile write back cache is used to reconstruct the write that was occurring when the crash occurred to insure consistent parity, so that only those blocks affected by the crash have to be reconstructed.

Abstract: Disclosed herein is a stacked skip list data structure for maintaining select nodes on multiple lists. The data structure includes a primary and a secondary skip list of nodes. Each node in the primary skip list uses at least one forward pointer in a primary array of forward pointers and provides a node level field for storing the level of such node, the level determined by the number of pointers being used. A secondary skip list is stacked on the primary skip list of nodes. It includes a subset (zero or more nodes) occurring on the primary skip list and utilizes zero or more unused forward pointers in the primary array as its forward pointers. Thus, a system agent performing operations on the secondary skip list utilizes the node level in the node level field as an index into the primary array of forward pointers to locate the secondary array of forward pointers.