FMMU: A Hardware-Automated Flash Map Management Unit for Scalable Performance of NAND Flash-Based SSDs

NAND flash-based Solid State Drives (SSDs), which are widely used from embedded systems to enterprise servers, are enhancing performance by exploiting the parallelism of NAND flash memories. To cope with the performance improvement of SSDs, storage systems have rapidly adopted the host interface for SSDs from Serial-ATA, which is used for existing hard disk drives, to high-speed PCI express. Since NAND flash memory does not allow in-place updates, it requires special software called Flash Translation Layer (FTL), and SSDs are equipped with embedded processors to run FTL. Existing SSDs increase the clock frequency of embedded processors or increase the number of embedded processors in order to prevent FTL from acting as bottleneck of SSD performance, but these approaches are not scalable. This paper proposes a hardware-automated Flash Map Management Unit, called FMMU, that handles the address translation process dominating the execution time of the FTL by hardware automation. FMMU provides methods for exploiting the parallelism of flash memory by processing outstanding requests in a non-blocking manner while reducing the number of flash operations. The experimental results show that the FMMU reduces the FTL execution time in the map cache hit case and the miss case by 44% and 37%, respectively, compared with the existing software-based approach operating in 4-core. FMMU also prevents FTL from acting as a performance bottleneck for up to 32-channel, 8-way SSD using PCIe 3.0 x32 host interface.