Patent ID: 7617371

Claim:
A storage controller for controlling data input/output between a host system and a storage device unit that stores data, the storage controller comprising: an adapter unit; a memory; and a remaining pool area amount confirmation unit, wherein the adapter unit writes or reads relevant data to or from the storage device unit in response to a data input/output request from the host system, wherein the memory stores system configuration information including a definition, set externally, of a virtual volume provided to the host system and a definition, set externally, of a real volume and a pool area, and a pool area management information including an entry of each data stored in the pool area, wherein the virtual volume is defined and set as an overall storage capacity larger than a real storage capacity of the real volume, wherein the real volume is assigned to a first part of the virtual volume and is defined and set as a logical volume for performing ordinary read/write operations from/to the storage device unit, wherein the pool area is assigned to a second part of the virtual volume and is used as a buffer storage area for storing data, wherein a third part of the virtual volume is not yet assigned to both the real volume and the pool area, wherein in response to each of data input requests designating an address of the third part of the virtual volume from the host system, the adapter unit allocates data of each of the data input requests to a storage area in the pool area transparently to the host system, according to a method in which the allocated storage area is reserved sequentially from a top address of the pool area, so that a range of addresses of the pool area is exceeded, wherein the adapter unit copies data stored in the pool area to the real volume transparently to the host system and cancels the entry of the data stored in the pool area from the pool area management information so that a range of addresses of the real volume is exceeded and the data stored in the pool area can be re-used, wherein the adapter unit communicates, to the host system, the storage capacity of the virtual volume based on the system configuration information stored in the memory in response to a storage capacity confirmation request from the host system, wherein the remaining pool area amount confirmation unit confirms a remaining amount of the pool area by calculating based on an address for a last effective entry, of data stored in the pool area, in the pool area management information, wherein the remaining pool area amount confirmation unit communicates the confirmed remaining amount of the pool area to a management console, and wherein the management console displays on a monitor the remaining amount of the pool area based on the communication from the remaining pool area amount confirmation unit.