Conventionally, a computer system providing a large-scale data storage service to a host device exists. This system is known to comprise a host device, a storage apparatus to which the host device is connected and a management device of the storage apparatus.
The storage apparatus manages multiple hard disks by the RAID (Redundant Array of Independent/Inexpensive Disks) method. Then, [the storage apparatus] logicalizes physical storage areas included in a large number of hard disks, and provides the same to the host device as logical volumes. The host device accesses the logical volumes to request data read and write.
As one type of such logicalization technology, there is Thin Provisioning. The storage apparatus has no physical storage area, and sets logical volumes in which the storage capacity is virtualized for the host device.
These logical volumes are called virtual volumes and, in accordance with the host device's write access to the virtual volumes, the storage apparatus sequentially assigns storage areas to the virtual volumes.
Therefore, this technology is effective compared with the method of assigning a large amount of storage areas in the logical volumes from the beginning in that the storage resources can be utilized efficiently.
This technology is described in U.S. Pat. No. 6,857,059, Japanese Unexamined Patent Application Publication No. 2003-015915, Japanese Unexamined Patent Application Publication No. 2006-338341, and Japanese Unexamined Patent Application Publication No. 2008-234158.
As the method for providing storage areas to virtual volumes, if the host device makes write access to a virtual volume, by assigning a storage capacity from the capacity pool comprising actual storage areas to the address of the virtual volume, [the storage apparatus] can save write data.
At this point, a “capacity pool” (also referred to simply as a “pool”) is defined and set, for example, as a set of multiple logical groups comprising actual capacity to be written to virtual volumes, and the multiple logical volumes belonging to the pool are respectively referred to as pool volumes.
Furthermore, US 2005/055603 discloses technology in which whether the access frequency to the saved data is high or low is determined and, if the access frequency is high, in accordance with physical characteristic information of pool volume media (the media type, RPM of the disk, and others), data is migrated, within the pool, to the pool volumes comprised of the media appropriate for high-speed processing.