On the Impact of Garbage Collection on Flash-Based SSD Endurance

Garbage collection has a profound impact on the write amplification in flash-based SSDs, which in turn may significantly reduce its life span. The unequal wear of data blocks further contributes to this reduced life span. In this paper we study two performance measures: the SSD endurance which assesses the life span of an SSD and the PE fairness which is a measure for the degree of unequal wear. We demonstrate, using a mean field model and simulation, how these measures are affected by the garbage collection algorithm, spare factor, etc. Numerical results indicate that under uniform random writes there is no need to implement a wear leveling technique. For hot and cold data we see that design choices that lower the PE fairness may still result in a higher SSD endurance, which suggests that one should not emphasize too much on equaling the wear.