Patent ID: 7035883

Claim:
A storage control system, comprising a plurality of physical storage devices with different attribute levels, a plurality of logical units provided on said plurality of physical storage devices, and a control device for writing data received from an external device to a logical unit selected from said plurality of logical units, wherein said plurality of logical units comprise one or more high level logical units provided on a physical storage device with a high attribute level, and one or more low level logical units provided on a physical storage device with an attribute level lower than said high attribute level, each of said plurality of logical units comprises a plurality of chunks, the plurality of chunks of said plurality of logical units comprise a plurality of high level chunks serving as said one or more high level logical units, and a plurality of low level chunks serving as said one or more low level logical units, at least one of said plurality of high level chunks and at least one of said plurality of low level chunks are dynamically-allocatable pool chunks, and when data in a first chunk selected from said plurality of chunks is written to a second chunk, said control device selects either a high level chunk or a low level chunk from said dynamically-allocatable pool chunks based on a status of use of said plurality of chunks, and writes the data in said first chunk to a selected chunk.