NV-DIMM: Unshackling Flash from its Controller


As NAND-flash-based solid-state storage devices (SSDs) continue their rise to dominance in arenas as diverse as embedded systems and high-performance computing, some of their original design tenets are worth revisiting. Specifically, in this work we reevaluate the "active" archetype of coupled storage and logic in SSDs. We provide qualitative and quantitative arguments that such coupling results in needless cost and complexity increases while simultaneously decreasing the flexibility available to applications and operating systems.

To cure these ills, we present two novel flash storage architectures, ON-DIMM and NV-DIMM. Both of our architectures unshackle NAND storage from their on-board controllers by moving to a new form factor (DIMM modules), a new interface (DDR3) on the main memory bus, and offloading the controller logic to a new non-volatile memory controller (NVMC) besides the host's existing main memory controllers. We extensively detail the architectural design of ON-DIMM and NV-DIMM, provide implementation insights, and experimentally evaluate via detailed simulation the power and performance characteristics of our architectures compared to traditional SSDs. For our more advanced architecture, NV-DIMM, we experimentally demonstrate improvements with respect to bandwidth and latency of 67% and 26%, respectively. Considering power, we show that ON-DIMM provides savings on the order of 67%, while NV-DIMM delivers power savings between 25% and 53% when compared against state-of-the-art traditional SSDs.