Consistency Without Ordering

Abstract

Modern file systems use ordering points to maintain consistency in the face of system crashes. However, such ordering leads to lower performance, higher complexity, and a strong and perhaps naive dependence on lower layers to correctly enforce the ordering of writes. In this paper, we introduce the No-Order File System (NoFS), a simple, lightweight file system that employs a novel technique called backpointer-based consistency to provide crash consistency without ordering writes as they go to disk. We utilize a formal model to prove that NoFS provides data consistency in the event of system crashes; we show through experiments that NoFS is robust to such crashes, and delivers excellent performance across a range of workloads. Backpointer-based consistency thus allows NoFS to provide crash consistency without resorting to the heavyweight machinery of traditional approaches.