A block clearing method for a non-volatile data-storage device operates by determining whether a number of data block programmed in a first mode is less than a threshold, selecting a spare block from a spare pool, programming a plurality of data from the selected data blocks into the selected spare block in a second mode, mapping a plurality of logical addresses of the data to a plurality of physical addresses on the selected spare block programmed in the second mode, and releasing the selected data blocks into the spare pool, wherein the selected spare block is able to be programmed in either the first mode or the second mode. Following the determining step, if the determination is true, the method selects a plurality of data blocks programmed in the first mode.