Patent ID: 8250327

Claim:
A storage apparatus, comprising: a first plurality of storage devices configuring a first plurality of storage regions; a second plurality of storage devices configuring a second plurality of storage regions; and a controller configured to: manage the first plurality of storage regions as a first storage pool; manage the second plurality of storage regions as a second storage pool; provide a first virtual volume to a host system, at least one of the first plurality of storage regions of the first storage pool being dynamically allocated to the first virtual volume in accordance with an access received from the host system for the first virtual volume; provide a second virtual volume to the host system, at least one of the second plurality of storage regions of the second storage pool being dynamically allocated to the second virtual volume in accordance with an access received from the host system for the second virtual volume; and manage an unused capacity in each of the first storage pool and the second storage pool, and wherein, upon the unused capacity of the first storage pool falling below a predetermined threshold value, the controller allocates a first storage region that is included in the second plurality of storage regions of the second storage pool and has not been allocated to the second virtual volume to the first storage pool so that the first storage region can be allocated to the first virtual volume, and wherein, upon a third plurality of storage devices configuring a third plurality of storage regions being added to the storage apparatus, the controller copies data stored in the first storage region to at least one of the third plurality of storage regions, adds the at least one of the third plurality of storage regions to the first storage pool, and returns allocation of the first storage region from the first storage pool to the second storage pool.