A first storage system is connected to a second storage system, and an external device within the first storage system is provided to a host as a device of the second storage system. The second storage system includes a cache control section having a cache adaptors, each controlling a disk and a cache,...http://www.google.com.au/patents/US7228380?utm_source=gb-gplus-sharePatent US7228380 - Storage system that is connected to external storage
