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 FPGAbased 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 out-perform flash-based arrays for the irregular (and frequently readdominated) 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.