Patent ID: 8738874

Claim:
A system, comprising: a first storage system configured to include a first CPU (central processing unit), a first memory, a plurality of first storage devices, the plurality of storage devices being configured to provide a plurality of first logical volumes to a server, and each of the plurality of first logical volumes being configured to include an operational volume and a differential volume; and a second storage system configured to include a plurality of second storage devices, the plurality of second storage devices being configured to provide a plurality of second logical volumes to a server, wherein the first memory is configured to store a remote copy program and a volume management program, the remote copy program and the volume management program being configured to be executed by the first CPU, wherein the volume management program is configured to: take snapshots of the operational volume from a first point in time to an n th point in time (n is an integer, where n≧3), for each address of the operational volume, if a first-time write operation occurs after taking the snapshot at an i th point in time before taking the snapshot at an (i+1) th point in time (i is an integer, where 1≦i≦n), copy data stored at the address of the operational volume to the differential volume before the write operation, for each address of the operational volume, manage a first bitmap and a second bitmap, the first bitmap indicating whether the write operation occurred after taking the snapshot at a (j−1) th point in time before taking the snapshot at a j th point in time (j is an integer, where 2≦j≦n), and the second bitmap indicating addresses in the differential volume where the data is copied, and wherein when remote copying of the snapshots from a k th point in time to the n th point in time (k is an integer, where 2≦k≦n−1) occurs, for each address of the operational volume, the volume management program is configured to provide a third bitmap indicating whether the write operation occurred after taking the snapshot at a (k−1) th point in time before taking the snapshot at the n th point in time based on the first bitmap, and the remote copy program is configured to specify data necessary to remote copy by checking whether a bit is on or off in the third bitmap for each address of the operational volume.