Patent ID: 7421550

Claim:
A storage system, in which a second storage control device and a third storage control device are each connected to a first storage control device, wherein the first storage control device comprises a first data volume, a first journal volume which manages the update history of the first data volume, and a first control portion which, when a higher-level device writes write data to the first data volume, generates journal data with a control number set for the write data, stores the journal data in the first journal volume, and transmits the write data to the second storage control device; the second storage control device comprises a second data volume associated with the first data volume, and a second control portion which stores the write data received from the first control portion to the second data volume, and stores the storage position of the write data in a differential management table; the third storage control device comprises a third data volume associated with the first data volume, a second journal volume associated with the first journal volume, and a third control portion which reads the journal data from the first journal volume and stores the journal data in the second journal volume, and which updated stored contents of the third data volume based on the journal data stored in the second journal volume; and upon switching from the first storage control device to the second storage control device, the second control portion transmits differential data to the third storage control device based on the differential management table, and stores the differential data in the third volume.