A Read Latency Variation Aware Independent Read Scheme for QLC SSDs

QLC flash-based SSDs has attracted growing interest and is expected to fit in read-intensive scenarios owing to its higher cost-effectiveness and shorter write endurance compared with the Triple-Level Cell (TLC) SSDs. Recently, new commands supporting independent reads such as Single Operation Multiple Locations (SOML) and Independent multi-plane (IMP) read are proposed to improve read performance. Unfortuantely, while independent read exhibits a significant performance improvement, we show in this paper that the exisiting approach fails to fully exploit its potential due to the larger read latency variation and more planes per die for current SSD architecture. Through a set of experiments, we demonstrate that the lack of a read latency variation aware machanism leads to low performance of independent read among a wide variety of workloads. To alleviate this issue, we propose LITA, which key idea is to combine read transactions with similar latency into one command. LITA includes (1) LIT, a latency variation aware transaction combination, (2) and TASAP, a latency variation aware transaction completion service. The experimental results show LITA can reduce read latency by 20.4% and 9.6% on average for 4-planes QLC SSDs under IMP and SOML, respectively.