Patent ID: 7827368

Claim:
A system to be coupled to a computer comprising: a storage subsystem including disk drives for storing data and a disk controller for controlling input/output of data to/from the disk drives; and a server subsystem coupled to the storage subsystem, wherein the disk controller is configured with a primary volume for storing data used by the computer, a differential volume for storing differential data between the primary volume and at least one differential snapshot of the primary volume, and a full-copy snapshot volume for storing a full-copy snapshot of the primary volume at a time when the a full-copy snapshot of the primary volume is taken, wherein the storage subsystem stores a differential block bitmap indicating a block in which data stored in the primary volume differs from data stored in the full-copy snapshot volume, wherein the storage subsystem stores differential block information for said at least one differential snapshot, the differential block information indicates storing locations of data of said at least one differential snapshot, wherein the server subsystem receives the differential block information from the storage subsystem, extracts differential data stored in a block identified by the differential block information from the differential volume, and creates a full-copy snapshot corresponding to the differential snapshot by using the data extracted from the differential volume and a copy of the primary volume.