Abstract: Accordingly, the present invention is directed to a method of managing data in a storage system. A method of performing a write to data storage system, including a first storage device and a second storage device, may include writing a first set of header information to a first storage device and a second storage device. The first set of header information includes a first sequence number and a second sequence number, in which the first set of header information includes a first sequence number incremented to indicate a change from the second sequence number. Data is written to the first storage device and the second storage device. Then, a second set of header information is written to a first storage device and a second storage device. The second set of header information includes a first sequence number and a second sequence number, in which the second set of header information includes a second sequence number incremented to correspond to the first sequence number.

Abstract: An improved shadow directory technique allocates storage space for directories in pairs in a logical volume. One of the spaces in each pair is used for a directory for locating data in the logical volume. The other space is reserved for an updated copy (shadow) of the directory if the directory is ever to be changed or updated. After the shadow directory is stored, it becomes a new directory for locating the data in place of the previous directory. The storage space containing the previous directory is unused, but retained as allocated for the next shadow directory, if needed. Since directory storage spaces are not deallocated, the improved shadow directory technique enables a simplified sequential-allocation storage management in a primarily data-add environment.

Abstract: In a storage system, such as a storage area network, a snapshot volume or one or more checkpoint volumes are formed from the same base volume using a single repository containing multiple images of data stored in the base volume. The first image is started with the formation of the snapshot volume or the first checkpoint volume and is filled with blocks of data copied from the base volume, thereby increasing in size within the repository, until the first image is stopped and the next image is started. The next image is then filled with blocks of data copied from the base volume until stopped. Thus, the blocks of data are copied only into the most recently created image within the repository. With the creation of each checkpoint volume, a new image is concurrently started in the same repository. Each checkpoint volume is dependent on the image that was created concurrently plus any images created thereafter.

Abstract: A method for allowing I/O requests to run concurrently during a rollback process, comprising the steps of (A) reading from and writing to an original volume and (B) running said I/O requests concurrently with the rollback process from a snapshot volume.

Abstract: A portion of a storage controller's cache memory is used as a virtual solid state disk storage device to improve overall storage subsystem performance. In a first embodiment, the virtual solid state disk storage device is a single virtual disk drive for storing controller based information. In the first embodiment, the virtual solid state disk is reserved for use by the controller. In a second embodiment, a hybrid virtual LUN is configured as one or more virtual solid state disks in conjunction with one or more physical disks and managed using RAID levels 1-6. Since the hybrid virtual LUN is in the cache memory of the controller, data access times are reduced and throughput is increased by reduction of the RAID write penalty. The hybrid virtual LUN provides write performance that is typical of RAID 0. In a third embodiment, a high-speed virtual LUN is configured as a plurality of virtual solid state disks and managed as an entire virtual RAID LUN.

Abstract: Methods and associated structure for enabling immediate availability of a disk array storage device. In particular, the methods and associated structure of the present invention permit access to a logical unit of a storage system immediately following creation of the logical unit. Initialization of the logical unit to initialize redundancy information therein proceeds in parallel with host system access to the storage space of the logical unit. The initialization process maintains a boundary parameter value indicative of the progress of the initialization process. Storage space above the boundary has had its redundancy information initialized while storage space below the boundary has not. Where an I/O request is entirely above the boundary, it is processed normally in accordance with the management of the logical unit. Where part of an I/O request is below the boundary, it is processed in a special manner that assures integrity of the redundancy data.

Abstract: An apparatus and method is disclosed which enables a host computer to adjust the caching strategy used for writing its write request data to storage media during execution of various software applications. The method includes the step of generating a caching-flushing parameter in the host computer. The cache flushing parameter is then transferred from the host computer to a controller which has a cache memory. Thereafter, a quantity of write request data is written from the cache memory to a storage medium in accordance with the cache-flushing parameter.

Abstract: A method and apparatus for increasing performance in a data processing system. The data processing system includes a plurality of storage devices and a backup storage device. The backup storage device is configured as a log device. Data is logged to the backup storage device after the backup storage device has been configured as a log device. In response to a failure of a storage device within the plurality of storage devices, the backup storage device is reconfigured to be used as a replacement for the failed storage device.

Abstract: A disk mirroring method operable in a disk array storage system for storing N images of a block of data across M drives (N>=3 and M>=N) to enhance flexibility in configuration of mirrored and non-mirrored LUNs. Each of the N copies of data resides on a different drive such that if N−1 drives fail, the original block of data is recoverable. Data blocks may be striped or non-striped over the plurality of drives. Where the data is striped, each segment of the stripe has at least two mirrored images on other drives of the array. The present invention therefore enhances configuration flexibility as compared to prior techniques because all drives of the array may be used for mirrored copies regardless of the number of drives. The present invention therefore does not waste space where, for example, an odd number of drives are configured in the LUN.

Abstract: Methods and associated apparatus for automatically synchronizing the operating code between a plurality of controllers. In a first embodiment after the spare controller is swapped into the storage subsystem, if the native controller determines that the spare controller's operating code is incompatible with the native controller's operating code, then the native controller notifies the spare controller that synchronization is required between both controllers. The native controller creates an image of its operating code including configuration parameters, and copies this "synch info" into a reserved area of cache memory. The spare controller's main CPU utilizes mirroring routines to copy the operating code and configuration parameters into a reserved area of its cache memory. After the transfer is complete, the spare controller's main CPU loads the operating code and configuration parameters into its program memory and resets itself to operate with the modified program memory.

Abstract: The invention relates to a method and apparatus for maintaining data/parity consistency in a RAID data storage system. The invention utilizes reserved disk storage space in the RAID array to log data necessary to restore data/parity consistency should an interruption event, such as a power failure, corrupt the data stored in a particular redundancy group. In one embodiment, the invention logs new data and new parity information to the reserved disk storage space before the new data and new parity information are written to the appropriate locations in the associated redundancy group. In this way, if an interruption event occurs when either the new data or the new parity information has already been written to the redundancy group but the other has not, the corresponding data and parity information stored in the reserved disk storage space can be used to restore data/parity consistency after the event has ended.

Abstract: The invention provides a method and apparatus for increasing the efficiency of data transfer between a host computer and a disk array in a RAID system. The invention operates by splitting up large I/O requests from the computer into smaller, more manageable pieces and processing the pieces as though they were individual I/O requests. In one embodiment, the invention keeps only a limited number of these smaller individual I/O requests "active" at any particular time so that a single large I/O request cannot preclude other I/O requests from making progress in the controller. Both the size of the smaller I/O request pieces and the limited number of these pieces which will be "active" at any one time may be tunable parameters. The invention improves the efficiency of data transfer between the host computer and the array of disk drives by providing for increased overlap of activity in the controller. This increased overlap of activity results in increased controller throughput.

Abstract: Methods and associated apparatus operable in a RAID subsystem to improve the speed and flexibility of initializing the subsystem by storing configuration and identification information in a reserved area on each disk drive in the subsystem. The reserved area on each disk drive of the disk array contains a unique identifier to identify the particular disk drive from all others and further contains group configuration information regarding all groups in which the particular disk drive is a member. The configuration and identification information is generated and written to each disk drive in the disk array when the particular disk drive is configured so as to be added or deleted from groups of the subsystem. Upon subsystem reset (e.g. power on reset or other reset operations), the RAID controller in the subsystem determines the proper configuration of the RAID groups despite temporary unavailability or physical relocation of one or more disk drives in the disk array.

Abstract: Methods and apparatus for the rapid generation of a snapshot copy of the data stored in a RAID storage subsystem. In addition to the users configured RAID logical units, the present invention provides for the definition within the RAID controller of a logical RAID level one device having an operational half comprising the users defined logical unit(s) and having a non-operational mirror component. The user access data stored on the RAID subsystem by direct access to the users defined logical units. When a user directs a snapshot copy request to the operational, user defined logical units, the RAID controller responds by temporarily configuring available storage capacity (e.g. spare disk drives) in the RAID subsystem to perform the function of the non-operational mirror component of the logical RAID level one device.

Abstract: Methods and apparatus for moving pinned data corresponding to a temporarily dead RAID device between the cache memory of a RAID subsystem and a log area. In response to detection of a dead RAID device within a RAID subsystem, the methods of the present invention move any pinned data from the cache memory of the RAID controller to a log area preferably allocated on the disk space of one or more operational RAID devices within the subsystem. In response to revival of the dead RAID device methods of the present invention restore the logged, pinned data from the log area of the operational RAID device(s) to the cache memory as dirty data ready for posting to the revived RAID device. The log area may be either permanently allocated within the RAID subsystem, or may be dynamically allocated in response to recognition of the dead RAID device and freed in response to revival of the RAID device.

Abstract: A method and corresponding controller apparatus for creating, updating and maintaining mapping information in a virtual mass storage subsystem. A request to manipulate a virtual block or cluster identifies a particular virtual block number. The virtual block number is mapped to a first physical block number by a direct calculation. A header data structure contained in the first physical block contains mapping information to locate other physical blocks associated with the virtual cluster. In addition to the header data structure, the first physical block contains a portion of the stored data for the corresponding virtual cluster. Additional physical blocks which stored the data of the virtual cluster are located from the mapping information in the header of the first physical block. The methods of the present invention provide improved performance and reduced buffer memory requirements in the virtual mass storage controller circuits of the subsystem as compared to prior approaches.

Abstract: Methods and associated data structures operable in a RAID subsystem to improve I/O performance. A two level cache data structure and associated methods are implemented with a RAID controller. The lower level cache comprises buffers holding recently utilized blocks of the disk devices. The upper level cache records which blocks are present in the lower level cache for each stripe in the RAID level 5 configuration. The upper level cache serves to reduce the overhead processing required of the RAID controller to determine which blocks are present in the lower level cache. Having more rapid access to this information by lowering the processing overhead enables the present invention to rapidly select between different write techniques to post data and error blocks from low level cache to the disk array. A RMW write technique is used to post data and error checking blocks to disk when insufficient information reside in the lower level cache.

Abstract: Methods and associated apparatus operable in a RAID subsystem having redundant disk array controllers to assure dual, redundant cache consistency while permitting operation of the RAID subsystem in response to host computer I/O requests. The methods and apparatus of the present invention provide for a process of initializing the redundant disk array controllers in response to a power-on reset cycle (or other similar reset cycles). The first controller partially initializes for processing of host requests then awaits the partial initialization of the second controller. After a brief timeout awaiting the second controller, or in response to an erroneous initialization of the second controller, the first controller configures itself to perform host computer I/O requests in a write-through mode (bypassing cache operations) until the second controller eventually initializes. Once both controller are initialized, the redundant caches are synchronized.

Abstract: A method of insuring recovery of a quantity write request data in a storage device having a plurality of controllers includes the steps of (1) providing a primary controller for storing the write request data received from a host device, (2) providing an alternate controller having a memory area allocated for use by the primary controller, (3) maintaining a first control block in the primary controller for indicating status of the write request data stored in the primary controller, and (4) maintaining a second control block in the alternate controller for indicating status of the write request data stored in the primary controller.