Patent ID: 7953952

Claim:
A computer which manages a storage system having a function to assign a real storage area to a virtual storage area specified by an access request, wherein the virtual storage area specified by the access request is one of a plurality of virtual storage areas which constitute the virtual volume; the assigned real storage area is an unassigned real storage area which has not been assigned to any virtual storage area among a plurality of real storage areas which constitute a storage area pool constituted by one or a plurality of real volumes; the virtual volume is a virtual logical volume; the real volume is a logical volume which is formed on the basis of the storage space of one or a plurality of physical storage devices of the storage system; and the computer comprises: a non-transitory memory; a specification module stored in the memory which specifies a virtual volume which is switched from a used target to an unused target; a release/non-release selection module stored in the memory which performs a release/non-release selection determining whether or not to release all of the real storage areas assigned to the specified virtual volume; and a release/non-release instruction module stored in the memory which creates a release/non-release instruction for controlling whether or not the storage system releases all of the real storage areas assigned to the specified virtual volume in accordance with the result of the release/non-release selection and transmits the created release/non-release instruction a virtual volume selection module stored in the memory which selects a virtual volume which constitutes an assignment target from a plurality of virtual volumes on the basis of whether the virtual volume is a virtual volume for which all of the real storage areas have been released; wherein the virtual volume selection module prioritizes the selection of a virtual volume for which all of the assigned real storage areas are released in cases where a virtual volume which is assigned to a higher level device with a low access frequency is selected and prioritizes the selection of a virtual volume for which all of the assigned real storage areas have not been released in cases where a virtual volume which is assigned to a higher level device with a high access frequency is selected.