Patent ID: 8407417

Claim:
A storage system coupled to one or more hosts, comprising: multiple types of physical storage device groups; and a storage control device, wherein the storage control device comprises, a storage resource, and a controller coupled to the multiple types of physical storage device groups, the storage resource, and the host(s), wherein the physical storage device group is configured of one or more physical storage devices, wherein the multiple types of physical storage device groups are the bases of multiple types of actual page groups, wherein the type of an actual page group is based on the attribute of the physical storage device group which is the base of the real page group, wherein the actual page group comprises multiple actual pages, wherein the controller provides one or more virtual volumes to the one or more hosts, wherein the virtual volume is a virtual logical volume configured of multiple virtual pages, wherein the virtual pages are virtual storage areas, wherein the actual pages are actual storage areas, wherein the storage resource stores allocation information, which is the information indicating which actual page is allocated to which virtual page, wherein the controller receives a write command from the host, identifies the virtual page as the write destination with reference to the write command, updates the allocation information to allocate a free actual page to the identified virtual page, and stores the write target data in the allocated actual page, wherein the actual page is an actual storage area, and the data stored in the actual page is stored in the physical storage device, which is the base of the actual page, wherein the controller performs migration processing that includes the processing (A) and (B) described below; (A) migrating the data stored in a first actual page in the actual page group of a first type to a second actual page in the actual page group of a second type, and (B) updating the allocation information to allocate the second actual page instead of the first actual page to the first virtual page, which is the virtual page as the allocation destination of the first actual page.