A storage system includes a host configured to transmit a write command and store write data in a buffer thereof, and a storage device. The storage device includes a nonvolatile memory including a plurality of blocks, each of the blocks including a plurality of sectors and each of the sectors logically divided into at least a lower page and an upper page for data storage, and a controller configured carry out a write operation to write the write data in the nonvolatile memory in response to the write command, and return a notice to the host acknowledging that the write operation is successful. When a portion of the write data are written in a lower page of a sector of a block and an upper page of the sector remains unwritten after the write operation, the host maintains the portion of the write data in the buffer even after receiving the notice.