High Performance Metadata Integrity Protection in the WAFL Copy-on-Write File System

We introduce a low-cost incremental checksum technique that protects metadata blocks against in-memory scribbles, and a lightweight digest-based transaction auditing mechanism that enforces file system consistency invariants. Compared with previous work, our techniques reduce performance overhead by an order of magnitude. They also help distinguish scribbles from logic bugs. We also present a mechanism to pinpoint the cause of scribbles on production systems. Our techniques have been productized in the NetApp® WAFL® (Write Anywhere File Layout) file system with negligible performance overhead, greatly reducing corruption-related incidents over the past five years, based on millions of runtime hours.