Patent ID: 7415573

Claim:
A storage system capable of communicating with a host computer, which issues a write request, said storage system comprising: a plurality of physical storage regions; a plurality of storage pools, which is constituted from two or more physical storage regions; a plurality of logical volumes, which is respectively associated to said plurality of storage pools; and a controller, which receives from said host computer a write request for a logical volume, allocates one or more physical storage regions inside a storage pool associated to said logical volume; and writes data in accordance with said received write request to said allocated one or more physical storage regions, wherein said plurality of physical storage regions comprises a physical storage region having one or more attributes, and a physical storage region having a plurality of attributes; a prescribed attribute is allocated to each of said plurality of storage pools, and said plurality of storage pools has overlapping parts, which overlap one another, and non-overlapping parts, which do not overlap one another; said overlapping part is an aggregate of overlapping physical storage regions constituting two or more storage pools of the plurality of storage pools, because of having the same plurality of attributes as the plurality of attributes respectively allocated to the plurality of storage pools; the non-overlapping part of the each storage pool is an aggregate of non-overlapping physical storage regions constituting only said each storage pool, because of having an attribute allocated to said each storage pool, and not having an attribute allocated to another storage pool; and said controller selects, from among a certain storage pool associated to a certain logical volume, a non-overlapping physical storage region, which is not allocated to said certain logical volume; allocates said selected non-overlapping physical storage region to said certain logical volume; migrates data inside said overlapping physical storage region allocated to said certain logical volume to said selected non-overlapping physical storage region; and releases the allocation of said migration-source overlapping physical storage region from said certain logical volume.