A storage system includes a master storage device for storing data based on a RAID level determined by a host, a slave storage device for storing the data according to a command distributed from the master storage device, and a controller hub for coupling the slave storage device to the master storage device, wherein the master storage device is further configured to transfer the command to the slave storage device through the controller hub when the master storage device receives a command processing request from the host, transmit a complete queue (CQ) to the host when operations of the master storage device and the slave storage device are completed in response to the command processing request, and request a host to allocate a capacity to each function in the master storage device and the at least one of the plurality of slave storage devices based on a reference capacity.