Patent ID: 7822928

Claim:
A storage device comprising: a first volume which stores data utilized by a host device, wherein the first volume is contained in at least one Serial Advanced Technology Attachment (SATA) disk drive; a second volume which stores a dual copy of at least a portion of the data contained in the first volume, and wherein the second volume is contained in at least one fibre channel (FC) disk drive such that the second volume has a quicker access time than the first volume; wherein the data is written into the first volume and second volume as dual copies responsive to a write command from the host device; a control part which performs control by extracting a life tag specifying a retention term during which the data is to be retained in the second volume having the quicker access time than the first volume, the control part managing, as update segment control information, a relationship among: a storage position of the corresponding data in the second volume, a storage position of the corresponding data in the first volume, the retention term of the corresponding data as specified by the life tag, and an elapsed term which has elapsed since the corresponding data was stored; a storage part including a cache memory, where the storage part is configured to temporarily store at least portions of the data in the cache memory, and then to store the at least portions of the data from the cache memory into the first volume and the second volume, wherein the storage part manages the update segment control information, and when the elapsed term of certain data exceeds the retention term of the certain data, the storage part nullifies the certain data in the second volume; and an access processing part which processes access requests from said host device.