SCORE: A Novel Scheme to Efficiently Cache Overlong ECCs in NAND Flash Memory
SCORE: A Novel Scheme to Efficiently Cache Overlong ECCs in NAND Flash Memory
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SCORE：一种在 NAND 闪存中高效缓存超长 ECC 的新方案
DOI：
10.1145/3291052
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发表时间：
2019
影响因子：
1.6
通讯作者：
Xie Changsheng
中科院分区：
文献类型：
--
作者：
Zhou You;Wu Fei;Lu Zhonghai;He Xubin;Huang Ping;Xie Changsheng
技术扩展和编程/擦除循环导致NAND闪存中的误码率增加。一些固态驱动器(SSD)采用超长纠错码(ECC)，其冗余大小超过闪存页面的备用区限制，以保护用户数据，以提高可靠性和寿命。但是，由于逻辑数据页及其ECC冗余存储在两个闪存页中，因此读取性能会显著降低。在本文中，我们发现与缓存数据相比，缓存ECC具有通过实现更高的命中率来减少闪存读取的巨大潜力。然后，我们提出了一种新的高效缓存过长ECC的方案，称为SCORE，以提高SSD的性能。将逻辑上连续的数据页的超过ECC冗余(称为ECC残留)分组为ECC页。Score对RAM进行分区，以工作负载自适应的方式缓存数据页和ECC页。最后，我们使用广泛的跟踪驱动模拟来验证SCORE。结果表明，SCORE在不牺牲数据命中率的情况下获得了较高的ECC命中率，与现有方案相比，在各种工作负载下的读取性能平均提高了22%。
Technology scaling and program/erase cycling result in an increasing bit error rate in NAND flash storage. Some solid state drives (SSDs) adopt overlong error correction codes (ECCs), whose redundancy size exceeds the spare area limit of flash pages, to protect user data for improved reliability and lifetime. However, the read performance is significantly degraded, because a logical data page and its ECC redundancy are stored in two flash pages. In this article, we find that caching ECCs has a large potential to reduce flash reads by achieving higher hit rates, compared to caching data. Then, we propose a novel scheme to efficiently cache overlong ECCs, called SCORE, to improve the SSD performance. Exceeding ECC redundancy (called ECC residues) of logically consecutive data pages are grouped into ECC pages. SCORE partitions RAM to cache both data pages and ECC pages in a workload-adaptive manner. Finally, we verify SCORE using extensive trace-driven simulations. The results show that SCORE obtains high ECC hit rates without sacrificing data hit rates, thus improving the read performance by an average of 22% under various workloads, compared to the state-of-the-art schemes.