Patent ID: 7296118

Claim:
A storage device comprising: a host interface connected to a host device and receiving data from the host device; a 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 differential data by providing in an 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 a specific per-generational virtual logical volume, and the specific per-generational virtual logical volume is used to create a remote copy, and wherein differential data between said first logical volume and said specific per-generational virtual logical volume is sent to another storage device as data for the remote copy.