Analysis on Heterogeneous SSD Configuration with Quadruple-Level Cell (QLC) NAND Flash Memory

This paper investigates optimal heterogeneously-integrated SSD configuration [1] with various non-volatile memories including quadruple-level cell (QLC) NAND flash [2] considering SSD performance, energy consumption and SSD endurance lifetime. Based on the design methodology of heterogeneous SSD composed of storage class memory (SCM), multi-level cell (MLC) and triple-level cell (TLC) NAND flash [1], this paper newly adds QLC and single-level cell (SLC) NAND flash as memory components and re-optimizes the memory configurations for various workloads. Four types of SSD are compared; 1) SLC/QLC NAND flash, 2) SCM/QLC NAND flash, 3) SCM/TLC/QLC NAND flash and 4) SCM/TLC NAND flash. As a result, performance of SCM/QLC NAND flash is about one-fourth of that of SCM/TLC NAND flash for all workloads because QLC NAND flash has 5.7 times longer write latency than TLC NAND flash. For cold workloads or high total SSD cost assumption, SCM/TLC NAND flash is recommended. For hot workloads with low total SSD cost assumption, however, SLC/QLC NAND flash is optimal with emphasis on better SSD endurance lifetime. Finally, SCM/TLC/QLC NAND flash is the best when considering performance and energy consumption. In particular, for write-hot application, prxy_0, SCM/TLC/QLC NAND flash achieves 67% higher IOPS/cost [1] than SCM/TLC NAND flash.