A storage apparatus comprises a disk device and a disk adapter for controlling the disk device. The disk adapter controls the disk device and forms a data volume and a pool volume, creates a data block for parity data, compresses write data and the created parity data, and stores a number of compressed data blocks equal to or less than a predetermined number and stores compressed parity data that are within a predetermined size in storage areas in an actual volume, and stores the remaining compressed data blocks of a number greater than the predetermined number and compressed parity data that exceed the predetermined size in storage areas in the pool volume corresponding to a virtual volume.