<p>Proposed are a computer system and a backup method that can improve backup efficiency. Data written to a first logical volume provided inside a first storage device are copied into a second logical volume provided inside said first storage device in response to a copy request from a host, the data copied to the second logical volume are transferred to a second storage device asynchronously with respect to the writing of data from the host to the first logical volume, and in the second storage device, the data transferred from the first storage device are written into a third logical volume provided inside said second storage device.</p>
