R&D: Decoupled SSD, Reducing Data Movement on NAND-Based Flash SSD

IEEE Computer Architecture Letters has published an article written by Jiho Kim, Myoungsoo Jung, and John Kim, School of Electrical Engineering, KAIST, Daejeon, Republic of Korea.

Abstract: “Modern NAND Flash memory-based Solid State Drive (SSD) is designed to support high bandwidth for I/O requests by exploiting various parallelism including multiple channels, multiple flash memory chips, and multiple planes. However, SSD system is utilized not only for general I/O requests but is also used during flash memory management processes (e.g., garbage collection). In particular, the sharing of system resources (e.g., system bus, DRAM) for I/O requests and garbage collection can cause performance degradation. In this letter, we address the system bus bottleneck and propose Decoupled SSD system that decouples the front-end (i.e. cores, system bus) with the back-end (i.e., flash memory) and provide an on-chip network to interconnect the controllers together. Our decoupled SSD enables advanced command (i.e. copy-back) to be exploited for efficient garbage collection; in particular, we propose to extend copy-back commands to enable global copy-back through the flash-controller interconnect to effectively decouple I/O path and garbage collection path. Our evaluations show that decoupled SSD results in up to 34.7% bandwidth improvement, for I/O traffic while achieving up to 69% speedup for garbage collection.“