High speed differential copy can be implemented in the fail-back after disaster recovery when the data of the primary site is protected safely. When a restore command is issued, the common snapshots of the snapshots of the primary site and the secondary site are extracted as the base snapshot by comparing the log tables of the primary site and secondary site. The volume of the primary site is rolled back with the extracted snapshots. The latest snapshot of the volume of the secondary site is transmitted to the primary site and it is applied to the volume of the primary site to synchronize the volumes of the primary site and the secondary site.
The present application is a continuation of application Ser. No. 11/271,821, filed Nov. 14, 2005 now U.S. Pat. No. 7,428,657; which claims priority from Japanese application JP 2005-305556, filed on Oct. 20, 2005, the content of which is hereby incorporated by reference into this application.
