Patent ID: 7127578

Claim:
A storage device having: a host interface connected to a host device and receiving data from the host device; memory connected to the host interface and saving data exchanged with the host device, and control information relating to the data exchanged with the host device; a plurality of disk interfaces connected to the memory and performing control to read and write the data exchanged with the host device to and from the memory; a plurality of disk drives connected to the plurality of disk interfaces and storing data sent from the host device based on control of the plurality of disk interfaces; and a control processor for controlling reading and writing of data to and from a first logical volume generated using storage areas of the plurality of disk drives performing control to write old data stored in the first logical volume into a second logical volume as per-generational differential data, and managing the differential data by providing in the area of the memory a snapshot management table for managing the relationships of the per-generational differential data stored in the second logical volume, wherein the snapshot management table is used to generate specific per-generational virtual logical volume, wherein the virtual logical volume is used to create a remote copy, wherein a first bitmap showing an area in which a differential occurred with respect to a previously created remote copy is created when updating the virtual logical volume, and a second bitmap showing the area of the differential data is created when writing the differential data to the second logical volume.