STAR: Improving Lifetime and Performance of High-Capacity Modern SSDs Using State-Aware Randomizer

Abstract: Although NAND flash memory has achieved continuous capacity improvements via advanced 3D stacking and multi-level cell technologies, these innovations introduce new reliability challenges, par- ticularly lateral charge spreading (LCS), absent in low-capacity 2D flash memory. Since LCS significantly increases retention errors over time, addressing this problem is essential to ensure the lifetime of modern SSDs employing high-capacity 3D flash memory. In this paper, we propose a novel data randomizer, STate-Aware Randomizer (STAR), which proactively eliminates the majority of weak data patterns responsible for retention errors caused by LCS. Unlike existing techniques that target only specific worst-case patterns, STAR effectively removes a broad spectrum of weak patterns, significantly enhancing reliability against LCS. By employing several optimization schemes, STAR can be efficiently integrated into the existing I/O datapath of an SSD controller with negligible timing overhead. To evaluate the proposed STAR scheme, we developed a STAR-aware SSD emulator based on characterization results from 160 real 3D NAND flash chips. Experimental results demonstrate that STAR improves SSD lifetime by up to 2.3x and reduces read latency by an average of 50% on real-world traces compared to conventional SSDs