In a memory apparatus, there are provided a mirror primary LU which is a memory region on a plurality of storage media formed of nD+1P, a mirror secondary LU that is a memory region on a plurality of storage media formed of mD+1P, an n-RAID control subprogram for performing RAID control of nD+1P, an m-RAID control subprogram for performing RAID control of mD+1P, and an LU mirror subprogram for performing writing into the mirror primary LU and mirror secondary LU and then effectuating duplexing or "mirroring" when a computer issues a data write request. The "m" and "n" are different integers more than or equal to 2.