When receiving a notification of an error detected by patrol processing of the device adaptor for a secondary disk apparatus, a first recovery processing unit reads out data corresponding to the error location from a normal primary disk apparatus and writes the data into the error disk apparatus to eliminate the error. If it is determined that the content of the error notification is abnormality of the block ID which is an identifier of the order of writing data, a second recovery processing unit retrieves a correct write address indicated by the identifier, compares data of the error disk apparatus with that of the normal disk apparatus, determines that a lost write exists in the case of mismatch, and eliminates the lost write by writing the data read out from the normal disk apparatus into the error disk apparatus.