STRAW: Stress-Aware WL-Based Read Disturbance Management for High-Density NAND Flash Memory

While NAND flash memory has continuously increased its storage density over decades, this progress has exacerbated the read-disturbance problem. In this work, we identify two fundamental limitations of existing read-disturbance management techniques that trigger read reclaim (RR) at the block granularity: (i) they overlook the heterogeneous reliability impact of read disturbance across individual wordlines (WLs), leading to unnecessary RR in many cases; and (ii) they address read disturbance only after disturbance-induced errors have already accumulated, which forces substantial RR-induced copy overheads in read-disturbance-prone modern NAND flash memory. To address these limitations, we propose STRAW (STRess-Aware Wordline-based read-disturbance management), a new technique that minimizes RR overheads through two key ideas: (i) stress-aware WL-based read reclaim, which monitors the accumulated read-disturbance effect on each WL and reclaims only heavily disturbed WLs, and (ii) stress-reduced read, which mitigates disturbance on valid WLs during each read operation by scaling pass-through voltages based on WL validity. Our experimental results using a modern SSD emulator show that STRAW reduces RR-induced page-copy overhead by 88.6% on average compared with the state-of-the-art technique.