Patent ID: 7506008

Claim:
A hierarchical storage apparatus comprising: a secondary storage unit that stores data in a second storage area; a primary storage unit that temporarily stores data in a first storage area, the data being exchanged between a host computer and the secondary storage unit; a virtual-storage-area setting unit that logically combines a portion of the first storage area and a portion of the second storage area to set a virtual storage area; and a data-storage control unit that sends the data stored in the virtual storage area to the host computer, when the data stored in the virtual storage area is requested by the host computer, wherein upon receiving a request to read the data stored in the virtual storage area from the host computer, the data-storage control unit reads the data from the portion of the first storage area belonging to the virtual storage area if the data requested is found in the portion of the first storage area belonging to the virtual storage area, and sends the data read to the host computer, and the data-storage control unit moves the data stored in the first storage area to the second storage area when the data is not referred to by the host computer for a predetermined period of time.