A storage group configured by a plurality of storage devices is configured by a plurality of storage sub-groups, and the respective storage sub-groups are configured from two or more storage devices. A sub-group storage area, which is the storage area of the respective storage sub-groups, is configured by a plurality of rows of sub-storage areas. A data set, which is configured by a plurality of data elements configuring a data unit, and a second redundancy code created on the basis of this data unit, is written to a row of sub-storage areas, a compressed redundancy code is created on the basis of two or more first redundancy codes respectively created based on two or more data units of two or more storage sub-groups, and this compressed redundancy code is written to a nonvolatile storage area that differs from the above-mentioned two or more storage sub-groups.