Re-Animator: Versatile High-Fidelity Storage-System Tracing and Replaying

Abstract

Modern applications use storage systems in complex and often surprising ways. Tracing system calls is a common approach to understanding applications' behavior, allowing offline analysis and enabling replay in other environments. But current system-call tracing tools have drawbacks: (1) they often omit some information---such as raw data buffers---needed for full analysis; (2) they have high overheads; (3) they often use non-portable trace formats; and (4) they may not offer useful and scalable analysis and replay tools. We have developed Re-Animator, a powerful system-call tracing tool that focuses on storage-related calls and collects maximal information, capturing complete data buffers and writing all traces in the standard DataSeries format. We also created a prototype replayer that focuses on calls related to file-system state. We evaluated our system on long-running server applications such as key-value stores and databases. Our tracer has an average overhead of only 1.8-2.3×, but the overhead can be as low as 5% for I/O-bound applications. Our replayer verifies that its actions are correct, and faithfully reproduces the logical file system state generated by the original application.