A storage system includes a first storage apparatus and a second storage apparatus including a second controller for sequentially transferring a copy of the part of the segments of data from a second buffer into a second storage device segment by segment in the same sequence as the second buffer have received a copy of the part of segments of data from a first buffer of the first storage apparatus. The second controller producing a backup copy in a backup data storage portion by copying a copy of one of the segments of the data stored in the second storage device that has been transferred from the second buffer into the second storage device while transferring a copy of the subsequent segment of the data next to said one of the segments of the data in the sequence from the second buffer to the second storage device.