Patent ID: 8209507

Claim:
A disk array controller comprising: a processor managing a primary volume, a pool volume and a snapshot of the primary volume at a certain timing, wherein the primary volume stores data sent from a host system and being paired with another volume in another disk array controller, wherein the primary volume and the pool volume stores a plurality of data of the snapshot that is supposed to be sent to the another disk array controller, wherein the processor controlling to send the plurality of data of the snapshot as a remote copy to the another disk array controller according to a remote copy procedure so that the another disk array controller stores the plurality of data of the snapshot as the remote copy in the another volume, and wherein first management information showing an area in which a differential occurred with respect to a previously stored remote copy is created when updating a virtual volume, and second management information showing the area in which the differential occurred having differential data between said primary volume and said virtual volume is created when writing the differential data to the another volume.