Patent ID: 8843724

Claim:
A computer system, comprising: a control device for processing a write access from a host computer; and at least one storage device, wherein the control device is configured to: provide an access target to be accessed by the host computer, provide a first pool, having one or more logical volumes provided by the at least one storage device and which are arranged in a hierarchy, provide a second pool, having one or more logical volumes provided by the at least one storage device and which are arranged in a hierarchy, assign a storage capacity from the one or more logical volumes of the first pool to a write destination area of the access target of a write request from the host computer, add at least one of the one or more logical volumes in the second pool to the first pool, according to a status of the first pool, and add at least one logical volume provided by the at least one storage device to the second pool, according to a status of the second pool, wherein the at least one logical volume of the second pool added to the first pool belongs to a same part of the hierarchy in the first pool as in the second pool.