This storage controller providing a volume for storing data transmitted from a host system includes a management unit for managing the data written in the volume with a first block area, or a second block area in the first block area which is smaller than the first block area; a snapshot acquisition unit for acquiring a snapshot of the volume at a prescribed timing; and a transfer unit for transferring the data of the volume acquired with the snapshot of the snapshot acquisition unit to an external device with the first block area or the second block area.