LUN CACHE method for FC-SAN memory system

The invention is an LUN CACHE method for an FC-SAN storage subsystem, and its character: it is implemented by a logic unit number cache (LUN CACHE) module operating in an embedded system of I/O processing nodes in the FC-SAN; it uses an improved CACHE displacement arithmetic to enhance the utilization ratio of CACHE, so as to complete the read-write operation in the I/O processing nodes by caching but not sending to a concrete SCSI device; uses a delayed write technique to update the data on the background, extremely improving the repose time; uses a mechanism of read-write lock to ensure a consistency of data sharing among multiple users; makes the LUN CACHE completely transparent for a user by the good design of interface devices. It is tested that the read-write operation performance is extremely enhanced by using the LUN CACHE than before.