Patent ID: 7181583

Claim:
A snapshot creating method for a storage system comprising a first volume storing data to be read or updated, a second volume storing update differences of the first volume, and a third volume storing a copy of the first volume, in which a snapshot of the first volume is created in response to a request from a client computer, the method comprising: receiving a snapshot creation request from the client computer; obtaining a usage ratio of the second volume by update differences at a time when the snapshot creation request is made; identifying a user who has made the snapshot creation request from a preset account; obtaining an update difference use history indicating use history of update differences in the second volume of the user; choosing, based on the usage ratio and the use history, one from different snapshot in which update differences of the first volume are written in the second volume and volume snapshot in which the third volume is synchronized with the first volume; and executing the chosen one of differential snapshot and volume snapshot.