A processor copies first information stored in a first storage to a backup volume. The processor stores management information when a first piece of the first information is updated to second information after the copy. The processor executes, when a failure occurs in the first storage, first restoration based on the management information and reference information stored in reference storages other than the first storage. The first restoration restores the second information to a spare storage. The processor executes second restoration based on the management information and the reference information. The second restoration restores third information to the spare storage. The processor stops the second restoration when a failure occurs in a second storage while the second restoration is being executed. The processor executes third restoration based on the first information stored in the backup volume and the management information. The third restoration restores fourth information to the spare storage.