Abstract: The present invention relates to a snapshot system for a data storage system including a host that communicates with a cache memory, source storage, target storage, and metadata, including a source storage for active data, a target storage to store migrated snapshot data, first metadata (e.g., bitmaps and log files with pointers) to indicate when and to locate where the first snapshot data is in the target storage, and second metadata (e.g., bitmaps and log files pointers) to indicate when and to locate where the second snapshot data is in the target storage wherein the first metadata and the second metadata locate the same snapshot data in the target storage.

Abstract: A process, apparatus, and system stores data check information on an electronic storage medium that uses standard sector data field sizes. The check information may include a cyclic redundancy check (CRC), a logical block address (LBA), a longitudinal redundancy check (LRC), state information, a sequence number, or other information to identify data state, misplacement, or corruption. The check information, instead of being appended to the data within the data sector, may be stored in an independent check sector. The check information corresponding to multiple data sectors may also be aggregated and stored in a single check sector. The process or apparatus may be incorporated in a storage system controller, a RAID controller, a software SCSI stack in a computer, an operating system, a storage device driver, or another appropriate application that interfaces with standard and commodity storage system components.

Abstract: A method, apparatus and program storage device for maintaining data consistency and cache coherency during communications failures between nodes in a remote mirror pair. A link between a mirror pair of storage systems is monitored. During a link failure between a first storage system and a second storage systems, reads and writes on the first and second storage systems are independently performed and write data and associated timestamps are maintained for the write data for each write in a queue on the first and second storage system. After link reestablishment, volume sets on the first and second storage systems are resynchronized using write data and associated timestamps.

Abstract: The present invention relates to a cache memory management system suitable for use with snapshot applications. The system includes a cache directory including a hash table, hash table elements, cache line descriptors, and cache line functional pointers, and a cache manager running a hashing function that converts a request for data from an application to an index to a first hash table pointer in the hash table. The first hash table pointer in turn points to a first hash table element in a linked list of hash table elements where one of the hash table elements of the linked list of hash table elements points to a first cache line descriptor in the cache directory and a cache memory including a plurality of cache lines, wherein the first cache line descriptor has a one-to-one association with a first cache line.

Abstract: A method, apparatus and program storage device for allowing continuous availability of data during volume set failures in a mirrored environment. Continuous servicing of input/output request for a volume set having failed on a primary array using either portions of the failed volume set or a mirrored volume set is provided. A determination is made whether the failed volume set can service the input/output request and continuous data availability is provided by using the failed volume set to process the input/output request when the failed volume set can service the input/output request, else using a remote mirrored volume set to process the input/output request.

Abstract: A mirror table that facilitates selective data coherency between local memory segments and remote memory segments includes a content addressable memory (CAM) and a random access memory (RAM). The CAM stores the addresses of local memory segments that are selected to be mirrored, and provides a segment index when presented with a segment address stored therein. The RAM stores one or more remote segment addresses for the mirrored segments along with additional data, and provides the remote segment addresses along with the additional data when presented with the segment index. A mirror link assembles and transmits an update packet comprising the remote segment addresses, a segment offset, the corresponding data, and the additional data to a remote destination. Each indicated remote address is updated with the corresponding data, thus maintaining data coherency between the selected local and remote memory segments.

Abstract: The present invention is a method and system for upgrading drive firmware on a drive within a distributed data storage system in a manner that is transparent and non-disruptive to the host system operations. The method and system allow for normal read and write operations to occur during the firmware upgrade process, even while the primary disk drive is off-line, through alteration of the controller read and write policies. A mapping file is created on a temporary storage device to reduce the necessary time period of the upgrade process. This time period is further reduced in a mirrored storage system or in a system having a spare drive, where a logging file is created to store the data diverted from the primary disk drive during the upgrade process. An advantage is the ability to maintain storage system redundancy during the upgrade process.

Abstract: A message tracker having a transfer monitor, a set of registers, and at least one arithmetic unit increases performance and reliability when transmitting or receiving messages within a computer system. A set of message parameters such as a current address, a remaining length, and a communicated length are stored within the set of registers. The transfer monitor observes data transfers on a multi-tenant bus in order to detect data transfers related to the message and provide an update signal. The message parameters within the registers are updated in response to the update signal. The process of detecting and updating is repeated until the entire message is transferred, and the message tracker then informs a control processor or process that communication of the message has occurred. To facilitate message coalescing, several message trackers may share a message queue that is configured to store message parameters corresponding to completed messages.

Abstract: A mirror table that facilitates selective data coherency between local memory segments and remote memory segments includes a content addressable memory (CAM) and a random access memory (RAM). The CAM stores the addresses of local memory segments that are selected to be mirrored, and provides a segment index when presented with a segment address stored therein. The RAM stores one or more remote segment addresses for the mirrored segments along with additional data, and provides the remote segment addresses along with the additional data when presented with the segment index. A mirror link assembles and transmits an update packet comprising the remote segment addresses, a segment offset, the corresponding data, and the additional data to a remote destination. Each indicated remote address is updated with the corresponding data, thus maintaining data coherency between the selected local and remote memory segments.

Abstract: A method and apparatus for cache coherency in storage system is disclosed. The invention maintains cache coherency in the controller system of the storage system in a manner to minimize the performance degradation to a host system, and to allow the caches to be coherent without requiring data to be written to the backing disks. Each controller manages an area of memory on the partner controller, but the area is managed dynamically and is done with the information about the partner controller. A first controller determines which mirror cache line on a second controller to copy data into, and then mirrors the data from a first controller cache line to a second controller cache line. A message is sent from the first controller to the second controller informing the second controller of cache meta data associated with the mirror cache line so that the cache line may be added to the second controller's hash table.