Patent ID: 7243196

Claim:
A disk array apparatus directly connected to a host computer and another disk array apparatus incapable of establishing a direct connection with the host computer in which data coming from the host computer is stored in a storage region as a result of addition of a storage region of the another disk array apparatus to a storage region of the disk array apparatus, the disk array apparatus comprising: a logical unit formation section for forming a plurality of logical units from the storage region of the addition result to be accessed by the host computer; a data writing section for writing, to each of the logical units, data coming from the host computer and the another disk array apparatus; a first check section for checking a validity of a reading request coming from the host computer for reading the data stored in the disk array and the another disk array apparatus; a data transfer section for, when the first check section determines that the data reading request is valid, transferring the data stored in each of the logical units to the host computer based on the data reading request; a second check section for checking a validity of an instruction coming from the host computer for forming a pair between, out of the plurality of logical units, the logical unit formed from the storage region of the disk array apparatus and the logical unit formed from the storage region of the another disk array apparatus; a pair formation section for forming the pair when the second check section determines that the instruction from the host computer is valid as a result of instruction check; and a copy section for, when the logical unit formed from the storage region of the disk array apparatus is accessed by the host computer for writing, copying writing data to the other logical unit forming the pair with the logical unit, wherein utilizing an interrelation between information about the plurality of logical units and information about the storage region as the addition result, the copy section copies the writing data to any actual storage region of the another disk array apparatus.