Consensus for Non-volatile Main Memory

Traditionally, computer storage has been separated into a hierarchy based on response time, volatility, and cost of media. This tiering is undergoing a significant upheaval as a new breed of memory technologies, termed Storage Class Memories (SCM), now make it feasible to replace several tiers of the hierarchy with a single, cost-effective, uniform type of memory/storage. To make large-scale SCM deployments practical, however, memory system designers will first need to solve the problem of how to guard against unavoidable storage wear-out and failures-problems traditionally absent from "main memory" and handled by software at leisurely timescales in the domain of storage. In this paper, we propose a novel approach to providing fault tolerance in SCM-based main memory. Our key insight is to treat memory as a distributed storage system and rely on data replication and a consensus protocol to keep the replicas consistent. Separate memory instances store replicated copies of the data, and we use a programmable network interconnect to provide fast consensus between the memory instances. Our initial experiments using software memory controller emulation demonstrate reasonable overhead over local memory reads and show great promise as scalable main memory.