R&D: Understanding and Optimizing Hybrid SSD With High-Density and Low-Cost Flash Memory

IEEE Xplore has published, in 2021 IEEE 39th International Conference on Computer Design (ICCD) proceedings, an article written by Liang Shi, School of Computer Science and Technology, East China Normal University, Shanghai, China, and Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan, China, Longfei Luo, Yina Lv, Shicheng Li, Changlong Li, and Edwin Hsing-Mean Sha, School of Computer Science and Technology, East China Normal University, Shanghai, China.

Abstract: “With the development of NAND flash technology, hybrid SSDs with high-density and low-cost flash memory have become the mainstream of the existing SSD architecture. In this architecture, two flash modes can be dynamically switched, such as single-level cell (SLC) mode and quad-level cell (QLC) mode. Based on evaluations and analysis of multiple real devices, this paper presents two interesting findings. They demonstrate that the coordination between the two flash-modes is not well-designed in existing architectures. This paper proposes HyFlex, which redesigns the strategies of data placement and flash-mode management of hybrid SSDs in a flexible approach. Specifically, two novel optimization strategies are proposed: velocity-based I/O scheduling (VIS) and garbage collection (GC)-aware capacity tuning (GCT). Experimental results show that HyFlex achieves encouraging performance and endurance improvement.“