A storage system having a processor that provides a volume to be an object of an input/output (I/O) request and executes I/O in response to the I/O request includes a valid volume provided to be the object of the I/O request, and an invalid volume not being provided to be the object. A plurality of invalid volumes includes invalid volumes of a plurality of types of capacities. The processor selects, when a volume creation request is received, the invalid volume on the basis of capacity according to the volume creation request to convert the selected invalid volume into a valid volume, and provides the validated valid volume.