In a disk array system having a plurality of spare drives, the storage areas of which are not wasted without being influenced by the physical boundaries thereof. There is defined one large spare parity group 104 which is composed of a plurality of spare drives 103, 103, . . . , and so on. A spare logic drive 202 having the same capacity as that of a faulty data drive 101B is cut out from a large spare logic drive 201 provided by the spare parity group 104, and the data of the faulty data drive 101B are copied to the cut spare logic drive 202. A virtual physical drive 206 corresponding to the spare logic drive 202 is defined and is incorporated instead of the faulty data drive 101B into a data parity group 102A. As a result, data of the faulty data drive 101B are saved in the virtual physical drive 206 (or the spare logic drive 202).