Wear-aware Out-of-order Dynamic Scheduling for NAND Flash-based Consumer Electronics

Because of the excellent performance and decreasing price of NAND flash, NAND flash-based solid-state drive (SSD) has been widely used as a storage system in consumer electronics. Moreover, modern consumer SSDs usually adopt a multichannel parallel structure. Thus, how to fully utilize the internal parallelism through IO scheduling is a key problem. The existing IO schedulers fail to solve the following: 1) the utilization of flash translation layer information to optimize the internal parallelism is not sufficient; 2) the wear of flash memory is not considered when allocating write requests. This article proposes a Wear-aware Out-of-order Dynamic Scheduling Algorithm (WODSA). First, according to the information of the flash translation layer, the max-parallel-based scheduling strategy is proposed to schedule the read requests to maximize read parallelism. Second, the wear-aware dynamic write allocation strategy is proposed based on the idle/busy state and wear degree of channels and chips. WODSA allocates write requests to channels and chips with less wear preferentially in a maximized parallel manner to achieve write parallelism and active dynamic wear-leveling. Experimental results show that compared with existing IO schedulers and dynamic wear-leveling algorithms, WODSA can improve both the average response time and wear-leveling in block-level and channel-level.