What is file system metadata?

Metadata comprises all the bookkeeping information in a file system: file sizes, permissions, modification and access times, etc. A workload that, e.g., opens and closes files in rapid succession leads to frequent metadata accesses, putting a lot of strain on any file server infrastructure. This is why a small number of users with “toxic” workload can slow down file operations to a crawl for everyone. Note also that especially parallel file systems are ill-suited for metadata-heavy operations.