One viable approach to deploy persistent memory (PM) in datacenters is to attach PM as self-contained devices to the network as disaggregated persistent memory, or DPM. DPM requires no changes to existing servers in datacenters; without the need to include a processor, DPM devices are cheap to build; and by sharing DPM across compute servers, they offer great elasticity and efficient resource packing.

We propose three architectures of DPM: 1) compute nodes directly access DPM (DPM-Direct); 2) compute nodes send requests to a coordinator server, which then accesses DPM to complete a request (DPM-Central); and 3) compute nodes directly access DPM for data operations and communicate with a global metadata server for the control plane (DPM-Sep). Based on these architectures, we built three atomic, crash-consistent data stores.

We introduce Distributed Shared Persistent Memory (DSPM), a new framework for using persistent memories in distributed datacenter environments. DSPM provides a new abstraction that allows applications to both perform traditional memory load and store instructions and to name, share, and persist their data. We built Hotpot, a kernel-level DSPM system that provides low-latency, transparent memory accesses, data persistence, data reliability, and high availability.

Get Hotpot here.

NVMM would be especially useful in large-scale data center environments, where reliability and availability are critical. However, providing reliability and availability to NVMM is challenging, since the latency of data replication can squander the low latency that NVMM can provide.

Mojim is a system that provides the reliability and availability that large-scale storage systems require, while preserving the performance of NVMM. Mojim achieves these goals by using a two-tier architecture in which the primary tier contains a mirrored pair of nodes and the secondary tier contains one or more secondary backup nodes with weakly consistent copies of data. Mojim uses highly-optimized replication protocols, software, and networking stacks. Our evaluation results show that surprisingly Mojim provides replicated NVMM with similar or even better performance than un-replicated NVMM (reducing latency by 27% to 63% and delivering between 0.4 and 2.7X the throughput). Mojim also outperforms MongoDB's replication system by 3.4 to 4X.