Patent ID: 8468302

Claim:
A storage system coupled to a host apparatus, the storage system comprising: a plurality of storage devices, each of which includes a plurality of real pages; and a controller, the controller being configured to: manage the plurality of storage devices as a pool; provide a virtual volume to the host apparatus, the virtual volume including a plurality of virtual pages to each of which a portion of the pool is allocated in accordance with a write command; distribute data written in a first virtual page to a first group of real pages, the first group of real pages being included in an allocated portion of the pool to the first virtual page, making up a redundant array and being selected from different storage devices; and migrate data stored in a first real page, which is a real page of the first group of real pages and belongs to a first storage device, to another storage device when the load of the first storage device is high, and not migrate data stored in another real page of the first group of real pages.