Research

Computing systems use dynamic random-access memory (DRAM) as main memory. As prior works have shown, failures in DRAM devices are an important source of errors in modern servers. To reduce the effects of memory errors, error correcting codes (ECC) have been developed to help detect and correct errors when they occur. In order to develop effective techniques, including new ECC mechanisms, to combat memory errors, it is important to understand the memory reliability trends in modern systems.

In this paper, we analyze the memory errors in the entire fleet of servers at Facebook over the course of fourteen months, representing billions of device days. The systems we examine cover a wide range of devices commonly used in modern servers, with DIMMs manufactured by 4 vendors in capacities ranging from 2GB to 24GB that use the modern DDR3 communication protocol.

We observe several new reliability trends for memory systems that have not been discussed before in literature. We show that (1) memory errors follow a power-law, specifically, a Pareto distribution with decreasing hazard rate, with average error rate exceeding median error rate by around 55; (2) non-DRAM memory failures from the memory controller and memory channel cause the majority of errors, and the hardware and software overheads to handle such errors cause a kind of denial of service attack in some servers; (3) using our detailed analysis, we provide the first evidence that more recent DRAM cell fabrication technologies (as indicated by chip density) have substantially higher failure rates, increasing by 1.8 over the previous generation; (4) DIMM architecture decisions affect memory reliability: DIMMs with fewer chips and lower transfer widths have the lowest error rates, likely due to electrical noise reduction; (5) while CPU and memory utilization do not show clear trends with respect to failure rates, workload type can influence failure rate by up to 6.5, suggesting certain memory access patterns may induce more errors; (6) we develop a model for memory reliability and show how system design choices such as using lower density DIMMs and fewer cores per chip can reduce failure rates of a baseline server by up to 57.7%; and (7) we perform the first implementation and real-system analysis of page offlining at scale, showing that it can reduce memory error rate by 67%, and identify several real-world impediments to the technique.