Patent ID: 8700853

Claim:
A storage apparatus which is connected via a network to a host which issues data I/O requests, comprising: storage devices of a plurality of types of varying performance; and a control unit configured to manage each storage area provided by each of the storage devices of a plurality of types by means of storage tiers of a plurality of different types, and to assign storage areas in predetermined units to virtual volumes from any storage tier among the storage tiers of a plurality of types in accordance with a data write request from the host, wherein, when there is an I/O request from the host, the control unit is configured to store data corresponding to the I/O request in predetermined units in a cache memory and to determine the storage tier of the storage area assigned to the virtual volume storing the data according to a mode of writing to the cache memory, wherein the mode of writing to the cache memory includes a cache fast write mode in which data is written only to the cache memory and the host is notified of writing completion, and wherein, when the mode of writing the data corresponding to the I/O request to the cache memory is the cache fast write mode, the control unit is configured to assign a storage area in a lower tier to the virtual volume storing the data.