Patent ID: 8661215

Claim:
A system, comprising: a first server including a first CPU (central processing unit) and a first memory; a first storage system including a plurality of first storage devices, the plurality of storage devices providing a plurality of first logical volumes to the first server, each first logical volume including an operational volume where the first server can perform read and write operations, and a differential volume; a second server; and a second storage system including a plurality of second storage devices, the plurality of second storage devices providing a plurality of second logical volumes to the second server, wherein the first memory stores a remote copy program and a volume management program, the remote copy program and the volume management program being executed by the first CPU, wherein the volume management program: takes 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), copies data stored at the address of the operational volume to the differential volume before the write operation, for each address of the operational volume, manages 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, 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 provides 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+1) th point in time based on the first bitmap, and the remote copy program specifies 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.