Onyx: A Prototype Phase Change Memory Storage Array

We describe a prototype high-performance solid-state drive based on first-generation phase-change memory (PCM) devices called Onyx. Onyx has a capacity of 10 GB and connects to the host system via PCIe. We describe the internal architecture of Onyx including the PCM memory modules we constructed and the FPGA-based controller that manages them. Onyx can perform a 4 KB random read in 38 µs and sustain 191K 4 KB read IO operations per second. A 4 KB write requires 179 µs. We describe our experience tuning the Onyx system to reduce the cost of wear-leveling and increase performance. We find that Onyx out-performs a state-of-the-art flash-based SSD for small writes (< 2 KB) by between 72 and 120% and for reads of all sizes. In addition, Onyx incurs 20-51% less CPU overhead per IOP for small requests. Combined, our results demonstrate that even first-generation PCM SSDs can outperform flash-based arrays for the irregular (and frequently read-dominated) access patterns that define many of today's "killer" storage applications. Next generation PCM devices will widen the performance gap further and set the stage for PCM becoming a serious flash competitor in many applications.