Patent ID: 7565501

Claim:
A storage controller providing a volume for storing data transmitted from a host system, comprising: a management unit for managing said data written into a first block area configured in said volume, or into a second block area configured in said first block area which is smaller than said first block area; a snapshot acquisition unit for acquiring a snapshot of said volume at a prescribed timing; and a transfer unit for transferring said written data of said volume and said snapshot acquired by said snapshot acquisition unit to an external device including a volume also configured with said first block area and said second block area to backup said written data and said snapshot therein, wherein data to be backed-up to the external device is transferred in a data size of the first or second block area depending upon a size of said data, said transfer unit transfers said data with said first block area when said data is not being managed with said management unit in said second block area, and when a total value of the areas of said second block area is greater than a prescribed threshold value, said management unit deletes all areas of said second block area that it is managing.