In a scale-out type storage in which multiple physical storage systems are provided collectively as a single virtual storage system, a logical path is established between the host computer and the virtual storage system so that input/output performance of the storage is not deteriorated, wherein during allocation of a volume to the virtual storage system, if a logical control unit (logical CU) establishing a logical path to a volume is unallocated, a logical CU and a volume is generated to a storage system having either a small number of allocated logical CUs or a small amount of used storage capacity. On the other hand, if there is a storage system having a logical CU already allocated thereto, a volume is generated in that storage system.