A storage device communicably coupled to a host device and another storage device includes a memory and a processor coupled to the memory and configured to: write, in a case where an area release command of a transaction volume is issued from the host device while data backup processing is performed with the another storage device using a generation-managed transmission buffer, the area release command in a first generation of the transmission buffer; and switch, in a case where a range of data write processing requested by the host device overlaps a range specified by the area release command written in the first generation, a generation of the transmission buffer from the first generation to a second generation.