Patent ID: 7802053

Claim:
A computer system, comprising: a first storage system coupled to a host computer and includes a first physical disk for storing data requested for data write by the host computer and a first disk controller for controlling to read/write data to the first physical disk; and a second storage system coupled to the first storage system and includes a second physical disk for storing data requested for data write by the first disk controller and a second disk controller for controlling to read/write data to the second physical disk, wherein the second disk controller provides a second volume to the first disk controller, wherein the first disk controller is configured to: define storage areas of the first physical disk as at least one first volume; define a first storage pool including the defined first volume and the provided second volume; provide to the host computer a first thin provisioning volume that is recognized as a volume having a capacity equal to or larger than a capacity of storage areas assigned from the first storage pool, assign, when a write request to the first thin provisioning volume is received from the host computer, any of one of storage areas of the first volume and storage areas of the second volume, which are included in the first storage pool, to the first thin provisioning volume; obtain an access status to the first thin provisioning volume from the host computer; migrate data having low access frequency among pieces of data stored in the storage areas of the first volume assigned to the first thin provisioning volume, to the storage areas of the second volume which can be assigned to the first thin provisioning volume; and migrate data having high access frequency among pieces of data stored in the storage areas of the second volume assigned to the first thin provisioning volume, to the storage areas of the first volume which can be assigned to the first thin provisioning volume, and wherein the first thin provisioning volume is thus assigned with both the storage areas of the first volume and the storage areas of the second volume, which are included in the first storage pool.