Patent ID: 7159087

Claim:
A storage system, in which a primary storage device having a primary volume and a secondary storage device having a secondary volume are connected, and which is capable of synchronizing said primary volume and said secondary volume by transmitting difference-related information relating to the difference between said primary volume and said secondary volume from said primary storage device to said secondary storage device, wherein said secondary storage device comprises: a differential transfer accommodation portion, which receives said difference-related information from said primary storage device; a generation management portion which creates generation management information based on said difference-related information received via said difference transfer accommodation portion; a generation management volume, which stores said created generation management information; and a generation restoration portion which restores the storage contents of a specified generation based on said secondary volume and on said generation management volume, wherein said generation management portion switches from a current generation to a new generation based on predetermined generation switching conditions which are conditions indicating how difference-related information from said primary storage device is to be divided according to generations, wherein said generation switching conditions includes at least one of time-related conditions and capacity-related conditions, and wherein said generation switching conditions can be set by a user in said secondary storage device.