This invention provides a secondary disk array device with functions for data management of a plurality of generations. The disk array device 1 of a primary site comprises remote copy functions. When updating of a primary volume 4 is performed by a host 3, differential data 5 occurs. The disk array device 1 performs remote-copying of the differential data 5 and difference management information to the disk array device 2 of a secondary site. The disk array device 2 receives the remote-copied data via a virtual secondary site 6. The differential data and similar is demarcated into generations, and is stored in a generation management volume 7. A secondary volume 8 stores the storage contents of the primary volume 4 at a prescribed point in time. By this means, remote copy functions can be used for data management of a plurality of generations within the disk array device 2. Generation management functions can be added to the system without interrupting operation of the primary disk array device 1, and without modification of specifications.