1. A data storage device which exchanges multi-stream data with a host, comprising: a nonvolatile memory device; a buffer memory configured to temporarily store data to be stored in the nonvolatile memory device or data read from the nonvolatile memory device; and a storage controller configured to receive from the host an access command for accessing segments of the multi-stream data, the accessing including reading the segments of the multi-stream data from or writing the segments of the multi-stream data to the nonvolatile memory device, wherein the storage controller is configured to determine access-requested segments to be sequential stream data based on a first multi-stream index included in the access command and the storage controller is configured to store the access-requested segments in the buffer memory, the access-requested segments being the segments of data for which access is requested in the access command, the multi-stream data including a plurality of data streams that correspond respectively to a plurality of multi-stream indexes, the first multi-stream index being one of a plurality of multi-stream indexes.