A mapping table H2F update technique for a FLASH memory is disclosed. In a disclosed data storage device, the controller updates a logical-to-physical address mapping table between a host and the FLASH memory in accordance with a group count of a buffer block of the FLASH memory. The group count reflects a logical address distribution of write data buffered in the buffer block and with non-updated logical-to-physical address mapping information. The higher the group count, the more dispersed the logical address distribution. In this manner, each update of the logical-to-physical address mapping table just takes a short time.