A storage system selects from a plurality of physical areas constituting a physical address space as copy source physical areas, one or more non-additionally recordable physical areas each including a fragmented free area, and also selects a recordable physical area as a copy destination physical area. The storage system then writes one or more pieces of live data from the selected one or more copy source physical areas to the free area of the selected copy destination physical area on a per-strip or per-stripe basis, sequentially from the beginning of the free area. If the size of the write target data is such that it is not possible to write the write target data to the free area on a per-strip or per-stripe basis, then the storage system pads the write target data, and writes the padded write target data to the free area on a per-strip or per-stripe basis.