Storage system based on nand flash and data retention improving method

The present invention relates to a storage system based on a NAND flash which comprises: at least one NAND flash memory including a plurality of blocks recording data; and a controller configured to execute data retention enhancing firmware to manage data. The controller records parity information for error correction in an arbitrary page of a preset specific block among the plurality of blocks by the execution of the firmware and performs scrubbing with respect to the data recorded in the plurality of blocks by using an error correction code and the parity information at a predetermined timing. Therefore, the storage system can increase durability of the NAND flash memory.