Understanding and Exploiting the Full Potential of SSD Address Remapping
Understanding and Exploiting the Full Potential of SSD Address Remapping
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了解并充分利用 SSD 地址重新映射的潜力
DOI：
10.1109/tcad.2022.3144617
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发表时间：
2022
期刊：
影响因子：
--
通讯作者：
Changsheng Xie
中科院分区：
文献类型：
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作者：
Qiulin Wu;You Zhou;Fei Wu;Hong Jiang;Jian Zhou;Changsheng Xie
重复写入在存储系统中普遍存在，其根源在于数据重复、日志记录和数据重定位等。随着基于闪存的固态硬盘 (SSD) 的广泛部署，重复写入会显着降低其性能和使用寿命。先前的研究提出了利用 SSD 内的地址重新映射实用程序来消除重复写入的创新方法。但是，重映射操作会修改逻辑到物理 (L2P) 地址映射表，而闪存上保留的物理到逻辑 (P2L) 映射保持不变。 L2P 和 P2L 映射之间的这种不一致可能会导致数据损坏，并且长期以来一直是使用 SSD 地址重新映射的主要障碍。在本文中，我们提出了一种新颖的 SSD 设计，称为 Remap-SSD-LH，它实现了 SSD 地址重新映射的全部潜力。它提供了一个重映射原语，允许主机软件和SSD固件以几乎零成本执行重复数据的逻辑写入。为了确保映射一致性以及快速映射查找，Remap-SSD-LH采用了基于混合存储的本地日志方案。为每个闪存垃圾收集单元维护本地日志，以记录由重映射操作引起的相关P2L映射变化。日志存储在小型非易失性 RAM (NVRAM) 中，例如电容器保护的 DRAM，并且如果 NVRAM 已满，则可以将其降级到闪存。我们通过三个案例研究在软件 SSD 模拟器上验证 Remap-SSD-LH：1）SSD 内重复数据删除； 2）SQLite日志； 3) F2FS 清理。实验结果表明，Remap-SSD-LH可以最大限度地、有效地利用地址重映射来提高SSD的性能和寿命。
Duplicate writes are prevalent in storage systems, originating from data duplication, journaling, and data relocations, etc. As flash-based solid state drives (SSDs) have been widely deployed, duplicate writes can significantly degrade their performance and lifetime. Prior studies have proposed innovative approaches that exploit the address remapping utility inside an SSD to eliminate duplicate writes. However, remap operations modify the logical-to-physical (L2P) address mapping table while the physical-to-logical (P2L) mappings persisted on flash memory remain unchanged. Such inconsistency between L2P and P2L mappings may cause data corruption and has long been a major obstacle to utilize SSD address remapping. In this article, we propose a novel SSD design, called Remap-SSD-LH, that realizes the full potential of SSD address remapping. It provides a remap primitive, which allows the host software and SSD firmware to perform logical writes of duplicate data at almost zero cost. To ensure mapping consistency as well as fast mapping lookups, Remap-SSD-LH employs a local log scheme based on hybrid storage. A local log is maintained for each flash garbage collection unit to record relevant P2L mapping changes induced by remap operations. The logs are stored in small nonvolatile RAM (NVRAM), e.g., capacitor-protected DRAM, and can be destaged to flash memory if NVRAM is full. We verify Remap-SSD-LH on a software SSD emulator with three case studies: 1) intra-SSD deduplication; 2) SQLite journaling; and 3) F2FS cleaning. The experimental results show that Remap-SSD-LH can maximally and efficiently exploit address remapping to improve SSD performance and lifetime.