A Novel Simulation Methodology for Accelerating Reliability Assessment of SSDs

Abstract

Reliability is an important factor to consider when designing and deploying SSDs in storage systems. Both the endurance and the retention time of flash memory are affected by the history of low-level stress and recovery patterns in flash cells, which are determined by the workload characteristics, the time during which the workload utilizes the SSD, and the FTL algorithms. Accurately assessing SSD reliability requires simulating several years' of workload behavior, which is time consuming. This paper presents a methodology that uses snapshot-based sampling and clustering techniques to help reduce the simulation time while maintaining high accuracy. The methodology leverages the key insight that most of the large changes in retention time occur early in the lifetime of the SSD, whereas most of the simulation time is spent in its later stages. This allows simulation acceleration to focus on the later stages without significant loss of accuracy. We show that our approach provides an average speed-up of 12X relative to detailed simulation with an error of 3.21% in the estimated mean and 6.42% in the estimated standard deviation of the retention times of the blocks in the SSD.