APPARATUS FOR HASHING CACHE ADDRESSES IN A CACHED DISK STORAGE SYSTEM

摘要

A storage subsystem including a cache (12) and backing storage (11) pairing is set associative under a hashing protocol which efficiently accommodates discontinuities in the backing storage (cylinder boundaries in a disk device) and preferential modules (index cylinders in multiple disk devices). The hashing preserves sequentiality between discontinuities and, by selective offsetting, ensures no hash overlap between preferred modules. The cache directory (30) comprises linked lists accessed by list from a table (27) accessed by the hash mechanism (34) which can be bypassed by reference to stored previous hash transforms (at 34) or by arithmetic determination.