Experiences with Formal Specification of Fault-Tolerant File Systems

Fault-tolerant, replicated file systems are a crucial component of today’s data centers. Despite their huge com-plexity, these systems are typically specified only in brief prose, which makes them difficult to reason about or ver-ify. This paper describes the authors ’ experience using for-mal methods to improve our understanding of and confi-dence in the behavior of replicated file systems. We wrote formal specifications for three real-world fault-tolerant file systems and used them to: (1) expose design similarities and differences; (2) clarify and mechanically verify consistency properties; and (3) evaluate design alternatives. Our expe-rience showed that formal specifications for these systems were easy to produce, useful for a deep understanding of system functions, and valuable for system comparison. 1