Patent ID: 8108644

Claim:
A storage control apparatus which is used by a write command issuing device, comprising: a real storage area management unit that manages a pool which has a plurality of real storage areas; a virtual volume constituted by a plurality of virtual storage areas, the real storage areas being assigned to the virtual storage areas in accordance with a write command issued by the write command issuing device; a storage area management table which is for managing relationships between the respective virtual storage areas and the respective real storage areas, and which is saved in the pool; and a virtual volume control unit that assigns a predetermined real storage area selected from among unassigned real storage areas among the respective real storage areas in the pool to the predetermined virtual storage area which corresponds with the write command among the respective virtual storage areas which constitute the virtual volume, wherein processing to update the storage area management table in the pool and processing to store write data, which correspond with the write command, in the predetermined real storage area are executed asynchronously, wherein the virtual volume control unit executes processing to update the storage area management table after assigning the predetermined real storage area to the predetermined virtual storage area and then executes processing to store the write data in the predetermined real storage area, and wherein the virtual volume control unit determines whether the write data are invalid write data after updating the storage area management table and, when a determination is made that the write data are invalid write data, determines whether the data already stored in the predetermined real storage are invalid data and, when a determination is made that the data already stored in the predetermined real storage area are invalid data, releases the predetermined real storage area and updates the storage area management table once again, and discards the invalid write data.