A method controls a storage system including a first storage apparatus including a first storage volume to store data therein, a second storage apparatus including a second storage volume to store data therein, the first and second storage apparatuses being communicably connected, and an information processor communicably connected to the first storage apparatus. The method includes the steps of transmitting by the information processor an identifier to identify the second storage volume in the second storage apparatus to the first storage apparatus, describing by the first storage apparatus the identifier in a data input/output request for the second storage volume and transmitting the data input/output request to the second storage apparatus, and executing by the second storage apparatus data input/output processing for the second storage volume identified by the identifier described in the data input/output request.