A first node performs copy (virtual copy) of address mapping between a virtual volume and a pool to a first virtual volume to create a third virtual volume in the first node. A second node performs mapping from a first pool volume in the second node to the third virtual volume in the first node, links an address of the first pool volume, which is mapped to the third virtual volume, to an address of a second virtual volume in the second node on a one-to-one basis, and performs log-structured write of the data in the second virtual volume to a second pool volume in the second node.