Patent ID: 7890720

Claim:
A storage system comprising: a disk device which includes: an original volume for storing data which is read/written by a host; and a snapshot volume for storing snapshot data of a plurality of snapshot generations of the original volume; and a storage control unit which includes: a processor unit; a memory storing information of each of the plurality of snapshot generations; a channel I/F that is coupled to the host; and a device I/F that is coupled to the disk device; and a tape device coupled to the storage control unit; wherein when the processor unit receives write data to a storage area of the original volume, the processor determines whether data stored in the storage area of the original volume is already copied to the snapshot volume or not; if the data stored in the storage area of original volume is not already copied to snapshot volume, the processor unit copies the data from original volume to the snapshot volume; when a use capacity of the snapshot volume is larger than a threshold amount, the processor unit indicates a specified snapshot generation; the processor unit migrates data of the specified snapshot generation from the snapshot volume to tape device; and the processor unit deletes information of the specified snapshot generation in the snapshot volume.