A data storage device includes a nonvolatile memory device configured to read and output a plurality of data chunks; and a data processing block configured to perform decoding on the data chunks, the data processing block comprising a sequencer configured to generate a decoding information on the data chunks; and a core circuit configured to perform normal decoding on a first data chunk among the data chunks based on the decoding information, and perform fast decoding on a second data chunk among the data chunks depending on whether a result of the normal decoding satisfies a fast decoding condition, wherein the fast decoding requires a shorter execution time than the normal decoding.