EddySuperblock: Improving NAND Flash Efficiency and Lifetime by Endurance-Driven Dynamic Superblock Management

Abstract

Solid-state drives (SSDs) are widely used in current storage systems. SSD manufacturers usually aggregate physical blocks across planes into one superblock to improve SSD performance. However, due to the wear endurance variations among blocks and pages, the standard superblock scheme leads to lifetime and space waste of SSDs. Superblock granularity also causes higher and more uncertain garbage collection overhead. To address these problems, this work proposes endurance-driven dynamic superblock management called EddySuperblock to provide a longer lifetime and higher space utilization with a faster and deterministic response time, which designs a dynamic superblock organization strategy that links free strong blocks into one superblock according to the real-time wear index of each block and introduces page-level wear management to further unlock the lifetime potential of pages. To reduce the high garbage collection overhead caused by superblocks, a nonblocking parallel garbage collection policy is proposed, which can reclaim space and serve requests simultaneously with low overhead. We conduct a set of experiments on a real hardware experiment platform. Both the proposed EddySuperblock and representative superblock schemes have been implemented on the experiment platform. The experimental results show that our scheme greatly reduces the average system response time by 47.6% and prolongs the lifetime by 75.6% compared with the state-of-the-art superblock scheme, and the final-state flash utilization reaches 95.4%. In the end, this article presents the application status of our work in real-world scenarios.