Abstract: A digital data storage subsystem stores data for use by digital data utilization device. The data as used by the digital data utilization device being organized in the form of variable-length records. The digital data storage subsystem includes a digital data storage device, a cache and a cache control. The digital data storage device has at least one fixed block storage unit for storing a predetermined amount of data, the storage unit storing at least one record and additional padding if the record does not comprise at least said predetermined amount of data. The cache including at least one cache slot which can accommodate the storage of the predetermined amount of data, that is, the amount which can be stored on the block storage unit of the digital data storage device.

Abstract: A shared system memory buffers data transfers between a plurality of host computers and a plurality of data storage devices. The system memory includes a cache memory and a number of queues and structures to facilitate performance. Management of a replacement queue within the system memory is based on the elapsed time and usage of the data element. If the elapsed time of a data element to be updated is less than a threshold, the data element will remain in the same location of the replacement queue; if the elapsed time is greater than the threshold, the data element is placed at the tail of the replacement queue. The threshold may be determined by dynamically monitoring the stress of the cache memory. The updating of the replacement queue is also affected by the number of times the data element has been accessed while in the replacement queue. The memory also includes a pending write data structure which is not part of the replacement queue.

Abstract: A shared system memory buffers data transfers between a plurality of host computers and a plurality of data storage devices. The system memory includes a cache memory and a number of queues and structures to facilitate performance. Management of a replacement queue within the system memory is based on the elapsed time and usage of the data element. If the elapsed time of a data element to be updated is less than a threshold, the data element will remain in the same location of the replacement queue; if the elapsed time is greater than the threshold, the data element is placed at the tail of the replacement queue. The threshold may be determined by dynamically monitoring the stress of the cache memory. The updating of the replacement queue is also affected by the number of times the data element has been accessed while in the replacement queue. The memory also includes a pending write data structure which is not part of the replacement queue.

Abstract: A shared system memory buffers data transfers between a plurality of host computers and a plurality of data storage devices. Management of the system memory includes establishing a replacement queue to facilitate performance. When a sequential operation is to be performed, the average fall through time of the data elements in the replacement queue is compared to a constant to determine the stress on the cache. If the cache is stressed, cache management establishes a microcache within the replacement cache. The microcache is used to stage data elements for the sequential operations and replaces data elements on a least recently used basis.

Abstract: A system and method for providing on-line, real-time, transparent data migration from a first data storage system to a second data storage system. The first data storage system which had previously been coupled to a host, network or other data processing system is disconnected from the host and connected to a second data storage system. The second data storage system is coupled to the host or data processing system. The second data processing system includes a data map or table which indicates which data elements are stored on the second data storage system and which corresponding data elements on the first data processing device have been copied to the second data storage system. When the host, network or data processing system requests data from a data storage system, the second data storage system determines whether or not the data is stored on the second or first data storage system. If the data is stored on the second data storage system, the data is made available to the requesting device.

Abstract: A shared system memory buffers data transfers between a plurality of host computers and a plurality of data storage devices. The system memory includes a cache memory and a number of queues and structures to facilitate performance. Management of a replacement queue within the system memory is based on the elapsed time and usage of the data element. If the elapsed time of a data element to be updated is less than a threshold, the data element will remain in the same location of the replacement queue; if the elapsed time is greater than the threshold, the data element is placed at the tail of the replacement queue. The threshold may be determined by dynamically monitoring the stress of the cache memory. The updating of the replacement queue is also affected by the number of times the data element has been accessed while in the replacement queue. The memory also includes a pending write data structure which is not part of the replacement queue.