A redundant recording disk device includes a first logical sub-disk and a second logical sub-disk. Mirrored redundant data are recorded such that a recording position on the first logical sub-disk and a recording position on the second logical sub-disk are positions on a corresponding radius and have a phase difference of 180 degrees around respective rotation axes of the disks with respect to one data. Therefore, the practical use of the disk device can be continued even when one recording surface is not usable because of a fault, and the access speed of the disk can be increased when there is no fault since the mirrored data which have been written with a predetermined phase-offset into the different recording surfaces may be read out in a parallel manner.