If it is determined in step S6 that the given period has not elapsed, or if step S8 has been ended, the storage controller 10 determines whether any SSD 20 has been added or not (step S9). Then the storage controller 10 may detect whether any SSD 20 has been added or not to a rack (not illustrated) loaded with the SSDs 20 or may check whether information that any SSD 20 has been added has been received or not from the management host device 3. If any SSD 20 has been added, the storage controller 10 carries out the first data distribution processing (see FIG. 16) including moving the data stored in the existing SSDs 20a to the added SSD 20b (step S10).

If any SSD 20 has not been added in step S8 or if step S9 has been ended, the storage controller 10 determines whether any deactivation request for deactivating the storage device 1 has been received or not at the management I/F 12 from the management host device 3 (step S11). The storage controller 10 returns to the processing of step S1 if any deactivation request has not been received, or ends the processing if any deactivation request has been received.

FIG. 12 is a flow chart for description of an example of the write processing of step S4 in FIG. 11.