When a failure occurs in a storage device, a backup unit specifies LUNs of a copy source and a copy destination to an operation volume for which a process is not taken over to another storage device and instructs to perform a copy. When a copy processing unit in the storage device receives a copy process to be performed in the operation volume, the copy processing unit performs the copy process by using the specified LUNs of the copy source and the copy destination. If an error occurs without the copy process being taken over to another storage device due to the occurrence of a failover, the backup unit acquires the LUNs of two volumes of a copy pair and the volumes each constituting each of cluster pairs. Then, the backup unit again performs the copy process by using the acquired LUNs.