Patent ID: 8447946

Claim:
A storage apparatus which provides a virtual volume to a host apparatus, and which, in response to a write request from the host apparatus with respect to the virtual volume, allocates storage areas dynamically to the virtual volume, the storage apparatus comprising: a plurality of memory apparatuses of a plurality of types; and a control unit for executing required data migration by monitoring an access frequency to each of a plurality of unit areas of the virtual volume and by controlling the corresponding memory apparatuses, wherein the control unit allocates a storage area having a superior response performance to unit areas having a higher access frequency the storage area being provided by the memory apparatus, wherein the plurality of unit areas in which the host apparatus reads data from and/or writes data to the virtual volume, and each of the plurality of unit areas comprises at least one of the plurality of storage areas, wherein the plurality of storage areas are dynamically allocated to the virtual volume in units of the storage areas of a predetermined size and, wherein the control unit; controls the corresponding memory apparatuses so that when data is migrated from a first storage area, provided by a first memory apparatus which can be rewritten a limited number of times, to a second storage area provided by second memory apparatus, the data is migrated to the second storage area without being deleted from the first storage area, manages updated units of storage areas of the data migrated from the first storage area to the second storage area after the data is migrated to the second storage area, and controls the corresponding memory apparatuses so that, when data which has been migrated from the first storage area to the second storage area is restored from the second storage area to the first storage area, the corresponding data still remaining in the first storage area is overwritten with the updated units of the storage areas of the data, the units of the storage areas being updated after migration to the second storage area.