US Patent 7415573 Storage system and storage control method

The storage system of the present invention comprises a plurality of physical storage regions comprising a physical storage region having one or more attributes, and a physical storage region having a plurality of attributes. A prescribed attribute is allocated for each pool constituted from two or more physical storage regions, and each such pool has overlapping physical storage regions, which overlap one another, and non-overlapping physical storage regions, which do not overlap one another. The overlapping physical storage region constitutes two or more pools of the plurality of pools because it has the same plurality of attributes as the plurality of attributes respectively allocated to the plurality of pools, but the non-overlapping physical storage region is not like this, and constitutes only one pool. A controller allocates, to a certain VOL, a non-overlapping physical storage region which is not allocated to this VOL from among a certain pool which is associated to the certain VOL, migrates data inside an overlapping physical storage region which is allocated to this VOL, to the non-overlapping physical storage region, and releases the allocation of the migration-source overlapping physical storage region from this VOL.