A data storage device includes a memory device and a memory controller. The memory controller configures a first memory block which is a TLC memory blocks as a data buffer, and accordingly configures a plurality of second memory blocks which are SLC memory blocks. The memory controller uses the first memory block to receive data and accordingly store same data in the second memory blocks as backup data. When an amount of available memory space of the first memory block is smaller than or equal to a predetermined amount, the memory controller determines whether any error has occurred in the data stored in the first memory block. When there is any error occurred in the data stored in the first memory block, the memory controller configures a third memory block and move the backup data stored in the second memory block to the third memory block.