Patent ID: 7606987

Claim:
A computer system comprising: a central processing unit (CPU); and a controller that is connected to an external storage unit and controls access to data by the CPU, the external storage unit including a storage area that includes a plurality of unit areas in at least a part of the storage area, each unit area being a respective discrete non-overlapping subdivision of said storage area and including a respective plurality of physical sectors, wherein the controller comprises: an access-area setting unit that dynamically specifies one of the unit areas, in which logical sectors of a set of logical sectors are assigned to respective physical sectors, as an access area for data, wherein for each of said unit areas, each physical sector within the respective unit area corresponds to a respective one of said logical sectors of said set of logical sectors; an addressing unit that, in a case where the CPU submits a data write request for the external storage unit, updates a first address specified as a write address in the data write request with a second address that represents a physical sector, within the unit area specified as the access area by said access-area setting unit, which corresponds to a logical sector of said set of logical sectors associated with the first address, and a valid-area changing unit that, at a predetermined time, migrates whole data in a first physical sector to a second physical sector, said second physical sector being within the unit area currently specified as the access area by said access-area setting unit, said first physical sector being within one of the unit areas that was specified as the access area before the unit area currently specified as the access area had been specified as the access area by said access-area setting unit, said first and second physical sectors corresponding to the same logical sector of said set of logical sectors.