The reliability measures in today's disk drive-based storage systems focus predominantly on protecting against complete disk failures. Previous disk reliability studies have analyzed empirical data in an attempt to better understand and predict disk failure rates. Yet, very little is known about the incidence of latent sector errors i.e., errors that go undetected until the corresponding disk sectors are accessed.Our study analyzes data collected from production storage systems over 32 months across 1.53 million disks (both nearline and enterprise class). We analyze factors that impact latent sector errors, observe trends, and explore their implications on the design of reliability mechanisms in storage systems. To the best of our knowledge, this is the first study of such large scale -our sample size is at least an order of magnitude larger than previously published studies -and the first one to focus specifically on latent sector errors and their implications on the design and reliability of storage systems.

Similar to software bugs, configuration errors are also one of the major causes of today's system failures. Many configuration issues manifest themselves in ways similar to software bugs such as crashes, hangs, silent failures. It leaves users clueless and forced to report to developers for technical support, wasting not only users' but also developers' precious time and effort. Unfortunately, unlike software bugs, many software developers take a much less active, responsible role in handling configuration errors because "they are users' faults."This paper advocates the importance for software developers to take an active role in handling misconfigurations. It also makes a concrete first step towards this goal by providing tooling support to help developers improve their configuration design, and harden their systems against configuration errors. Specifically, we build a tool, called SPEX, to automatically infer configuration requirements (referred to as constraints) from software source code, and then use the inferred constraints to: (1) expose misconfiguration vulnerabilities (i.e., bad system reactions to configuration errors such as crashes, hangs, silent failures); and (2) detect certain types of errorprone configuration design and handling.We evaluate SPEX with one commercial storage system and six open-source server applications. SPEX automatically infers a total of 3800 constraints for more than 2500 configuration parameters. Based on these constraints, SPEX further detects 743 various misconfiguration vulnerabilities and at least 112 error-prone constraints in the latest versions of the evaluated systems. To this day, 364 vulnerabilities and 80 inconsistent constraints have been confirmed or fixed by developers after we reported them. Our results have influenced the Squid Web proxy project to improve its configuration parsing library towards a more user-friendly design.

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