Data storage device and method for operating data storage device

A method for operating a data storage device, comprising:

• allocating a flash memory of a data storage device to provide space to receive data downloaded from a host, wherein the flash memory provides a plurality of first-type blocks and a plurality of second-type blocks, the first-type blocks comprise single level cells, and the second-type blocks comprise multi-level cells;
• and
• allocating the flash memory to provide the first-type blocks to receive the data downloaded from the host before the data storage device is soldered to a printed circuit board,
• wherein:
• when the number of first-type blocks allocated to receive the data downloaded from the host exceeds an upper limit, the flash memory is changed to provide the second-type blocks to receive the data downloaded from the host;
• and
• when detecting that the flash memory has been changed to provide the second-type blocks to receive the data downloaded from the host, a fail message is returned to the host to indicate unreliable write operations prior to soldering.