Patent ID: 8775730

Claim:
A storage apparatus providing a first virtual volume and a second virtual volume, each having a plurality of virtual storage areas, to a host system comprising: a plurality of disk drives; and a controller that is configured to: configure a plurality of error correcting code (ECC) groups with the plurality of disk drives, each of the plurality of ECC groups being allocated a plurality of storage areas as a capacity from the plurality of disk drives; allocate the capacity respectively from the plurality of ECC groups to at least one of the plurality of virtual storage areas of the first virtual volume and the second virtual volume dynamically in accordance with a received request from the host system; manage configuration information that represents a first capacity, a second capacity, a third capacity, and a fourth capacity, the first capacity being a capacity allocated to the first virtual volume and belonging to a first ECC group, the second capacity being a capacity allocated to the first virtual volume and belonging to a second ECC group, the third capacity being a capacity allocated to the second virtual volume and belonging to the first ECC group, and the fourth capacity being a capacity allocated to the second virtual volume and belonging to the second ECC group; and execute a rearranging process in which: comparing the first capacity to the second capacity, and if the first capacity is larger than the second capacity and a difference between the first capacity and the second capacity is larger than a threshold partially based on the configuration information, at least one storage area of a plurality of first storage areas is migrated to at least one storage area of a plurality of second storage areas in order to make the difference between the first capacity and the second capacity smaller, and comparing the third capacity to the fourth capacity, and if the third capacity is larger than the fourth capacity and a difference between the third capacity and the fourth capacity is larger than a threshold partially based on the configuration information, at least one storage area of a plurality of third storage areas is migrated to at least one storage area of a plurality of fourth storage areas in order to make the difference between the third capacity and the fourth capacity smaller.