Patent ID: 7536592

Claim:
A storage system comprising: a physical snapshot execution part which writes data that has been updated into both a primary storage device and a secondary storage device; a logical snapshot execution part which writes input data into said primary storage device, and which writes differential data between said data and data prior to updating into said secondary storage device; an update data search part which performs a search in order to ascertain whether or not data that is to be updated is present in said primary storage device involved in a snapshot data preparation request when such a preparation request is received from a higher-level device; a data updating amount judgment part which judges whether or not the amount of updated data in said primary storage device is greater than a specified value when said update data search part finds that update data is present in said primary storage device; and a snapshot execution part selection part which selectively drives said physical snapshot execution part when said data updating amount judgment part judges that said amount of updated data is greater than said specified value, and which selectively drives said logical snapshot execution part when said data updating amount judgment part judges that said amount of updated data is less than said specified value, or when no updated data is present in said storage device.