Disclosed is an image forming apparatus including: at least three storing devices; a detecting unit; and a control unit, wherein the striping is carried out by using all of the storing devices, and the mirroring is carried out by using at least two of the storing devices except at least one storing device. When one of the storing device is failed, in case that the mirroring was carried out by using the failed storing device, the mirroring is continued by using the one storing device which is not used for carrying out the mirroring instead of the failed storing device. The striping is carried out by using all of the storing devices except the failed storing device.