This paper (by Peng Huang, Chuanxiong Guo, Lidong Zhou, Jacob R. Lorch, Yingnong Dang, Murali Chintalapati, and Randolph Yao) occurred in HotOS 2017. The paper is an easy read at 5 pages, and considers the fault-tolerance problem of cloud scale systems. Although cloud provides redundancy for masking and replacing failed components, this becomes useful only if those failures can be detected. But some failures that are partial and suble failures remain undetected and these "gray failures" lead to major availability breakdowns and performance anomalies in cloud environments. Examples of gray failures are performance degradation, random packet loss, flaky I/O, memory thrashing/leaking, capacity pressure, and non-fatal exceptions. The paper identifies a key feature of gray failure as differential observability . Consider the setup in Figure 2. Within a system, an observer gathers information about whether the system is failing or not. Based on the observations, a reactor takes a...
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