Reducing write amplification in flash by death-time prediction of logical block addresses

Abstract

Flash-based solid state drives lack support for in-place updates, and hence deploy a flash translation layer to absorb the writes. For this purpose, SSDs implement a log-structured storage system introducing garbage collection and write-amplification overheads. In this paper, we present a machine learning based approach for reducing write amplification in log structured file systems via death-time prediction of logical block addresses. We define death-time of a data element as the number of I/O writes before which the data element is overwritten. We leverage the sequential nature of I/O accesses to train lightweight, yet powerful, temporal convolutional network (TCN) based models to predict death-times of logical blocks in SSDs. We leverage the predicted death-times in designing ML-DT, a near-optimal data placement technique that minimizes write amplification (WA) in log structured storage systems. We compare our approach with three state-of-the-art data placement schemes and show that ML-DT achieves the lowest WA by utilizing the learnt I/O death-time patterns from real-world storage workloads. Our proposed approach results in up to 14% reduction in write amplification compared to the best baseline technique. Additionally, we present a mapping learning technique to test the applicability of our approach to new or unseen workloads and present a hyper-parameter sensitive study.