mergerfs/mkdocs/docs/terminology.md

Terminology

• disk, drive, disk drive: A physical data storage device. Such as a hard drive or solid-state drive. Usually requires the use of a filesystem to be useful. mergerfs does not deal with disks.
• filesystem: Lowlevel software which provides a way to organize data and provide access to said data in a standard way. A filesystem is a higher level abstraction that may or may not be stored on a disk. mergerfs deals exclusively with filesystems.
• path: A location within a filesystem. mergerfs can work with any path within a filesystem and not simply the root.
• branch: A base path used in a mergerfs pool. mergerfs can accomidate multiple paths pointing to the same filesystem.
• pool: The mergerfs mount. The union of the branches. The instance of mergerfs. You can mount multiple mergerfs pools. Even with the same branches.
• relative path: The path in the pool relative to the branch and mount. foo/bar is the relative path of mergerfs mount /mnt/mergerfs/foo/bar.
• function: A filesystem call such as open, unlink, create, getattr, rmdir, etc. The requests your software make to the filesystem.
• category: A collection of functions based on basic behavior (action, create, search).
• policy: The algorithm used to select a file or files when performing a function.
• path preservation: Aspect of some policies which includes checking the path for which a file would be created.
• out-of-band: out-of-band in our context refers to interacting with the underlying filesystem directly instead of going through mergerfs (or NFS or Samba).