Time-efficient Garbage Collection in SSDs

TL;DR

This paper introduces two new garbage collection strategies for SSDs that significantly reduce runtime while maintaining low write amplification, enhancing SSD lifespan and performance.

Contribution

The paper proposes two optimized garbage collection strategies that improve runtime efficiency of cost-benefit methods with minimal impact on write amplification.

Findings

Runtime improved by up to 24 times compared to original strategies

Maintains low write amplification similar to cost-benefit approach

Effective in multi-channel, multi-TByte SSDs

Abstract

SSDs are currently replacing magnetic disks in many application areas. A challenge of the underlying flash technology is that data cannot be updated in-place. A block consisting of many pages must be completely erased before a single page can be rewritten. This victim block can still contain valid pages which need to be copied to other blocks before erasure. The objective of garbage collection strategies is to minimize write amplification induced by copying valid pages from victim blocks while minimizing the performance overhead of the victim selection. Victim selection strategies minimizing write amplification, like the cost-benefit approach, have linear runtime, while the write amplifications of time-efficient strategies, like the greedy strategy, significantly reduce the lifetime of SSDs. In this paper, we propose two strategies which optimize the performance of cost-benefit, while (almost) preserving its write amplification. Trace-driven simulations for single- and multi-channel SSDs show that the optimizations help to keep the write amplification low while improving the runtime by up to 24-times compared to the original cost-benefit strategy, so that the new strategies can be used in multi-TByte SSDs.