A digital data storage subsystem comprises a cache memory, a digital data store and a host adapter. The cache memory includes a plurality of cache slots, each of which caches digital data from the digital data store for access by the host adapter. The digital data store includes a disk drive, in which data is stored in the form of variable- or fixed-length records. The storage controller identifies one of said data storage sections as constituting a current owner of respective ones of the cache slot, and is responsive to record staging requests to selectively transfer records from the data storage section identified as the owner of said at least one cache slot to said cache slot for caching. In staging records for the current owner, the storage controller may, but need not, over-write records that were previously staged in the cache slot for previous owners. The host adapter is responsive to access requests requesting access to a record such that, if the record for which access is requested is in a cache slot, it can access the record, whether the record's data storage section is the current owner of the cache slot, or one of a predetermined number of previous owners of the cache slot for which the record was not overwritten for a subsequent owner. On the other hand, if the record is not in a cache slot, which may occur if, for example, it has not been staged in a cache slot or it was staged in a cache slot but has been overwritten while the cache slot was owned by a subsequent owner, the host adapter will generate a record staging request for processing by the storage controller.
|G06F 12/ 08 A I
|Published - 4 May 1999