Patent ID: 7917805

Claim:
A storage system comprising: a plurality of RAID groups constituted from a plurality of physical storage devices; a plurality of real areas constituting a capacity pool, which is created on the basis of storage areas of said plurality of RAID groups; mapping information denoting which real areas are allocated to which virtual areas in a virtual volume constituted from a plurality of virtual areas; real area management information denoting which real areas are allocated to which virtual areas; an input/output controller, which receives a write request from a computer, allocates a real area in said capacity pool to a virtual area in the virtual volume specified in this write request, writes data conforming to this write request to the allocated real area, and associates, in mapping information and real area management information, information denoting the allocated real area with information denoting the virtual area that is the allocation destination of this real area; and a restore controller, which references said real area management information to determine whether or not a low-reliability real area, which is a real area for which reliability has been lowered by occurrence of a failure in a certain physical storage device, and which belongs to the RAID group comprising this certain physical storage device, has been allocated to a virtual area, the restore controller not carrying out a data restore process for a low-reliability real area that has not been allocated to a virtual area, but carrying out a data restore for a low-reliability real area that has been allocated to a virtual area.