A storage includes: host interface units; file control processors which receives a file input/output request and translates the file input/output request into a data input/output request; file control memories which store translation control data; groups of disk drives; disk control processors; disk interface units which connect the groups of disk drives and the disk control processors; cache memories; and inter-processor communication units. The storage logically partitions these devices to cause the partitioned devices to operate as two or more virtual NASs.