Patent ID: 7111026

Claim:
A method for acquiring snapshot data in a storage system in such a manner to create a plurality of snapshot generations, said storage system including a plurality of storage devices and a controller which controls operation of said storage system including receiving data from an information processing device and controlling writing and reading of data from and to said storage devices, the method implemented by said controller included in said storage system comprising the steps of: providing said storage system with a plurality of differential data storage regions, each corresponding to one of the snapshot generations and each storing differential data of a time period corresponding to the one of the snapshot generations, each differential data storage region holding differential data accumulated for the purpose of restoring original data to one or more of said storage devices, from the start of a time period, in place of update data updated to said one or more storage devices during that time period, for at least two or more time periods, said differential data being held in said differential data storage regions corresponds to said time periods; receiving from said information processing system a snapshot processing command which is used to create a new snapshot generation; comparing an amount of update data received after the time period of a most recent snapshot generation to a predetermined amount of data to determine whether the amount of update data is equal to or more than the predetermined amount of data; creating the new snapshot generations if the amount of update data is equal to or more than the predetermined amount of data, thereby executing snapshot processing based on said snapshot processing command; and issuing, in response to the executing of snapshot processing, a report to said information processing device indicating that snapshot processing was executed.