A storage system where storage areas are provided to host systems using a conventional AOU technique, the storage system being able to reduce power consumption by the storage resources allocated to pools and prevent the shortening of the life expectancy of the storage resources. In the storage system, data storage devices defined as belonging to the pools are allocated to virtual volumes. Allocation is performed in accordance with access by the hosts. The data storage devices are powered off before being allocated to the virtual volumes and powered on after being allocated.