Data written in the primary logical volume of the first storage device are transmitted to the third storage device via the second storage device, the data being written in the same location as the primary logical volume within the secondary logical volume in the third storage device; when transmission of the data stops among the first to the third storage devices, the respective second storage device and the third storage device manage locations in the secondary logical volume where the data held thereby are to be written; and, when transmission of the data resumes among the first to the third storage devices, the locations in the secondary logical volume managed by the respective second and the third storage devices are aggregated, the data to be written in the respective aggregated location in the secondary logical volume being transmitted from the first storage device to the third storage device via the second storage device.