Patent ID: 8793461

Claim:
A storage system being coupled to a computer, the storage system comprising: a plurality of storage devices configuring a plurality of logical volumes which make up a pool; and a controller configured to: manage a plurality of storage regions provided by the pool, each logical volume of the pool including storage regions of the plurality of storage regions; provide a plurality of virtual volumes, each of which is associated with the pool and has a plurality of virtual storage regions, a storage region of the plurality of storage regions being allocated to a virtual storage region of the plurality of virtual storage regions in accordance with a write command from the computer, and send a predetermined data pattern to the computer when the controller receives a read request from the computer to a virtual storage region to which a storage region is not allocated, wherein, upon receipt of a first command specifying a first virtual volume of the plurality of virtual volumes, the controller is configured to: examine specific storage regions in the pool, which are storage regions allocated to the first virtual volume, of the plurality of storage regions, to determine whether data stored in the specific storage regions matches the predetermined data pattern; and if data stored in a first storage region allocated to a first virtual storage region of the first virtual volume matches the predetermined data pattern, cancel the allocation of the first storage region to the first virtual storage region, wherein, upon receipt of the first command specifying the first virtual volume, the controller is configured to not examine storage regions in the pool, which are allocated to a second virtual volume of the plurality of virtual volumes which is different from the first virtual volume, of the plurality of storage regions.