A method of operating a storage device with a memory includes partitioning an entire area of a first namespace into at least one area based on a reference size. The partitioning is performed in response to a namespace creating request from a host that includes size information corresponding to the entire area of the first namespace. The method further includes partitioning a logical address space of the memory into a plurality of segments, allocating a first segment of the plurality of segments to a first area of the at least one area, and storing mapping information of the first area and the first segment. A size of the logical address space is greater than a size of a physical storage space of the memory identified by the host.