An external storage system connected to a host apparatus includes a plurality of storage devices, and a control unit for controlling the above described plurality of storage devices, wherein the above described control unit manages a storage space formed by the above described plurality of storage devices...http://www.google.cl/patents/US5584008?utm_source=gb-gplus-sharePatent US5584008 - External storage unit comprising active and inactive storage wherein data is stored in an active storage if in use and archived to an inactive storage when not accessed in predetermined time by the host processor
