An operating method of a storage device includes simultaneously buffering first data in a first nonvolatile memory device and a second nonvolatile memory device, simultaneously buffering second data in the second nonvolatile memory device and a third nonvolatile memory device, performing a parity operation on the first data and the second data in the second nonvolatile memory device to generate a parity, and programming the first data, the second data, and the parity into the first nonvolatile memory device, the third nonvolatile memory device, and the second nonvolatile memory device, respectively.