Patent ID: 8447941

Claim:
A computer system, comprising: a storage system comprising: a first virtual logical volume which is a copy source volume; a second virtual logical volume which is a copy destination volume of the first virtual logical volume; and a plurality of storage devices upon which a plurality of tiers are based at least in part, each tier comprising a plurality of storage areas, wherein I/O (Input/Output) performance of each of the plurality of tiers is different; and a controller configured to control data migration, wherein the controller is configured to allocate an unallocated storage area among the plurality of storage areas to a write destination area in the first or second virtual logical volumes; wherein the controller is configured to migrate first data from a first storage area allocated to the first virtual logical volume in a first tier of the plurality of tiers to a second storage area in a second tier of the plurality of tiers, which is different from the first tier, using a migration policy which defines the relationship between the plurality of tiers and I/O frequency ranges and allocate the second storage area to the first virtual logical volume on behalf of the first storage area, wherein the controller is configured to migrate second data from a third storage area in a third tier of the plurality of tiers, allocated to the second virtual logical volume, and associated with the first storage area, to a fourth storage area in a fourth tier of the plurality of tiers which is different from the third tier, by using an associated policy which defines a migration destination tier of data in an associated destination storage area that is the same as a migration destination tier of data in an associated source storage area, and allocate the fourth storage area to the second virtual logical volume on behalf of the third storage area.