<p>When write processing once interrupted is restarted, if new data is stored in a nonvolatile memory 34 and regeneration of parity is impossible because data can not be read out normally from a third disk device (for instance 32-2) other than a disk device (for instance 32-1) in which new data is to be written and a disk device (for instance 32-5) for parity, a data writing unit 113 in a special write executing unit 110 overwrites the new data stored in the nonvolatile memory 34 at a specified write position of an appropriate disk device (for instance 32-1).</p>
