Adaptive Differential Wearing for Read Performance Optimization on High-Density nand Flash Memory

With cost reduction and density optimization, high-density NAND flash memory has been widely deployed in data centers and consumer devices. However, this trend has significantly degraded the read performance and lifetime of high-density NAND flash memory during the last decade. Previous works proposed to optimize flash lifetime with wear leveling (WL) and optimize read performance with reliability improvement. Although WL can improve flash lifetime, it leads to the reliability of all blocks in 3-D NAND flash decreasing simultaneously. The reliability and read performance will be degraded with flash wearing. To solve this problem, an adaptive differential wearing (ADWR) scheme is proposed to optimize the read performance and lifetime in this work. The basic idea of ADWR is to determine the size of the high-reliability area to serve hot reads based on workload characteristics. Specifically, first, a differential wearing scheme is proposed to construct different reliability areas based on the characteristics of the data. Second, a lifetime model is constructed for the ADWR to clarify the lifetime impact. Based on this, a lifetime optimization scheme is proposed to improve the flash lifetime. Finally, a differential refresh scheme is proposed to reduce the impact of read disturbance on read performance. The experiments on real-life workloads show that ADWR achieves encouraging read performance optimization with negligible impacts on the lifetime of 3-D TLC NAND flash memory.