Exploiting workload dynamics to improve SSD read latency via differentiated error correction codes

Abstract

This article presents a cross-layer codesign approach to reduce SSD read response latency. The key is to cohesively exploit the NAND flash memory device write speed vs. raw storage reliability trade-off at the physical layer and runtime data access workload dynamics at the system level. Leveraging runtime data access workload variation, we can opportunistically slow down NAND flash memory write speed and hence improve NAND flash memory raw storage reliability. This naturally enables an opportunistic use of weaker error correction schemes that can directly reduce SSD read access latency. We develop a disk-level scheduling scheme to effectively smooth the write workload in order to maximize the occurrence of runtime opportunistic NAND flash memory write slowdown. Using 2 bits/cell NAND flash memory with BCH-based error correction correction as a test vehicle, we carry out extensive simulations over various workloads and demonstrate that this developed cross-layer co-design solution can reduce the average SSD read latency by up to 59.4% without sacrificing the write throughput performance.