Disclosed is a storage device which includes a nonvolatile memory device and a controller. The controller communicates with a host through a first port, communicates with an external storage device through a second port, and controls the nonvolatile memory device based on first mapping information. The controller is configured to receive second mapping information from the external storage device, receive first write data from the host and to selectively transmit first write data to the external storage device based on the second mapping information.