A storage device includes a nonvolatile memory device and a storage controller. The nonvolatile memory device includes a first memory region having a first write speed and a second memory region having a second write speed different from the first write speed. The storage controller includes an internal buffer and stores data from an external host in the first memory region by priority in a first mode. The storage controller controls a data migration operation by performing a read operation-transfer operation to read a second data that is pre-stored in the first memory region by a first unit and to transfer the first unit of data to a data input/output (I/O) circuit of the nonvolatile memory device a plurality of times and by storing the second data transferred to the data I/O circuit in the second memory region.