A data storage device includes a memory device and a controller. The memory device includes a first buffer, a second buffer, and a backup memory block. The first buffer is an MLC block and the second buffer is an SLC block. The controller is coupled to the memory device, receives a write command to write predetermined data in the memory device and determines whether the predetermined data has to be written into different buffers. When the controller determines that the predetermined data has to be written into different buffers, the controller writes a portion of the predetermined data that has been written in one or more predetermined pages of the first buffer into the backup memory block.