Tolerating File-System Mistakes With EnvyFS

The authors introduce EnvyFS, an N-version local file system designed to improve reliability in the face of file-system bugs. EnvyFS, implemented as a thin VFS-like layer near the top of the storage stack, replicates file-system metadata and data across existing and diverse commodity file systems (E.g., ext3, ReiserFS, JFS). It uses majority-consensus to operate correctly despite the sometimes faulty behavior of an underlying commodity child file system. Through experimentation, they show EnvyFS is robust to a wide range of failure scenarios, thus delivering on its promise of increased fault tolerance; however, performance and capacity overheads can be significant.