A method and system for enhancing efficiency in power failure handling in flash memory devices is disclosed. The method includes the controller of a storage device receiving a page of data, selecting a block having a desired back-up cost and copying previously stored data in the selected block to a back-up block prior to writing the received page to the selected block based on a category of the previously stored data. The system includes non-volatile memory having a plurality of operative blocks, at least one spare block and a controller. The controller is configured to receive a page of data, select an operative block in the memory having a desired back-up cost, and copy previously stored data in the selected block to a spare block based on a category of the previously stored data prior to writing the received page to the selected block.