Gemini: A Novel Hardware and Software Implementation of High-performance PCIe SSD

In the era of big data, high-bandwidth and high-concurrency architecture of storage systems is urgently needed. Due to the superiority in power consumption, random access rate and shock resistance, NAND flash memory is popularly adopted in enterprise-class storage systems, and gradually takes the place of traditional hard disk. However, this kind of superiority is not off-the-shelf. Several factors, such as out-of-place update and limited erase/program cycles, have hindered the applicability of flash memory in existing storage systems. Therefore, to fully exploit flash memory's advantages, this paper proposes a high-performance PCIe SSD, Gemini, and depicts its principles in hardware and software implementation. Our proposed Gemini features several hardware and software optimizations, including PBFTL (the page to block mapping FTL), Dysource (a synchronous-interface flash channel controller with the out-of-order scheduling strategy), a customized I/O stack, the scatter/gather DMA and the multi-queue architecture. What's more, an FPGA-based prototype of Gemini with 2 TB storage capacity is implemented for verification. In experiment, Gemini achieves a maximum read bandwidth of 3.6 GB/s and a maximum write bandwidth of 1.08 GB/s for 64 KB data access. It can also provide remarkable processing rates over 580,000 IOPS and 270,000 IOPS, with regard to 4 KB random read and write respectively.