Patent ID: 8108630

Claim:
A storage apparatus comprising: a storage unit; a controller for providing a host computer with a storage area in the storage unit as a plurality of volumes, and controlling access from the host computer to the volumes; and memory in which management information for managing the volumes is set, the controller being configured to control, in accordance with the management information, writing write data sent from the host computer to the volumes, wherein the plurality of volumes includes a primary volume that the host computer write-accesses and a plurality of secondary volumes that functions as a replicated volume for the primary volume, and the plurality of secondary volumes comprises a main-volume to which write data for write access from the host computer directed to the primary volume is written and a plurality of sub-volumes that is subordinate to the main-volume, wherein the main-volume forms a synchronous pair with the primary volume and the sub-volumes each form an asynchronous pair with the primary volume, and wherein the controller is configured to write, upon receipt of the write access from the host computer, the write data to the primary volume and the main-volume, and then write the write data written to the main-volume to the plurality of sub-volumes later in background processing, wherein when the synchronous pair between the primary volume and the main-volume is split state, the controller selects one of the sub-volumes and changes the asynchronous pair between the primary volume and the selected sub-volume to a synchronous pair, so that the controller is configured to write, upon receipt of the write access from the host computer, the write data to the primary volume and the selected sub-volume, and then write the write data written to the selected sub-volume to the plurality of sub-volumes other than the selected sub-volume later in the background processing.