STRAW: A Stress-Aware WL-Based Read Reclaim Technique for High-Density NAND Flash-Based SSDs

TL;DR

STRAW is a novel, stress-aware, word-line level read-reclaim technique for NAND flash SSDs that significantly reduces unnecessary reclaim operations by tracking and targeting heavily disturbed word lines, improving reliability and efficiency.

Contribution

The paper introduces STRAW, a word-line level read-reclaim method that accounts for heterogeneous read disturbance effects, unlike traditional block-level approaches.

Findings

Reduces read-reclaim-induced page writes by 83.6%.

Achieves this with negligible storage overhead.

Effectively manages heterogeneous reliability impacts on each word line.

Abstract

Although read disturbance has emerged as a major reliability concern, managing read disturbance in modern NAND flash memory has not been thoroughly investigated yet. From a device characterization study using real modern NAND flash memory, we observe that reading a page incurs heterogeneous reliability impacts on each WL, which makes the existing block-level read reclaim extremely inefficient. We propose a new WL-level read-reclaim technique, called STRAW, which keeps track of the accumulated read-disturbance effect on each WL and reclaims only heavily-disturbed WLs. By avoiding unnecessary read-reclaim operations, STRAW reduces read-reclaim-induced page writes by 83.6\% with negligible storage overhead.