US Patent 7979663 Storage apparatus having unused physical area autonomous management function

A physical extent assurance unit manages correspondence of a logical disk accessed from a host computer with physical extents. A data pattern generation response unit generates a predetermined data pattern, and returns this data pattern in response to a data request from the host computer. A pattern matching unit checks the data pattern of a storage area every access to storage media or periodically. When the entire area of the assured physical extent defines the predetermined data pattern, the pattern matching unit deleted the logical disk allocation of the assured physical extent.