4.4 KiB
Compatibility and Integration
What filesystems can be used as branches?
ext4, btrfs, xfs, f2fs, zfs, nfs, etc.
On the surface any filesystem should work but there could be issues with non-POSIX compliant filesystems such as vfat, ntfs, cifs, exfat, etc. When directories need to be created or files moved by mergerfs if the filesystem returns errors due to not supporting certain POSIX filesystem features it could result in the core functions failing.
Since mergerfs is not generally used with non-POSIX filesystems this has not been a problem for users and there are some checks for known edgecases but it is possible some are not accounted for. If use with a filesystem results in issues please file a ticket with the details.
Can I use mergerfs without SnapRAID? SnapRAID without mergerfs?
Yes. They are completely unrelated pieces of software that just happen to work well together.
Does mergerfs support CoW / copy-on-write / writes to read-only filesystems?
Not in the sense of a filesystem like BTRFS or ZFS nor in the overlayfs or aufs sense. It does offer a cow-shell like hard link breaking (copy to temp file then rename over original) which can be useful when wanting to save space by hardlinking duplicate files but wish to treat each name as if it were a unique and separate file.
If you want to write to a read-only filesystem you should look at overlayfs. You can always include the overlayfs mount into a mergerfs pool.
Can mergerfs run via Docker, Podman, Kubernetes, etc.
Yes. With Docker you'll need to include --cap-add=SYS_ADMIN --device=/dev/fuse --security-opt=apparmor:unconfined or similar with
other container runtimes. You should also be running it as root or
given sufficient caps to allow mergerfs to change user and group
identity as well as have root like filesystem permissions. This
ability is critical to how mergerfs works.
Also, as mentioned by hotio,
with Docker you should probably be mounting with bind-propagation
set to slave.
How does mergerfs interact with user namespaces?
FUSE does not have any special integration with Linux user namespaces
used by container runtime platforms like Docker, Podman, etc. The
uid/gid values passed to mergerfs will be the host level values rather
than that seen inside the container. Meaning root in a container
with user namespaces configured will not be root to mergerfs. Same
with any other uid/gid. Meaning your permissions on your branches must
work with the translated values from the id mapping.
It is generally recommended to not use user namespacing / id mapping given the complication it introduces.
Can mergerfs be used with NFS root squash?
If mergerfs is pooling a NFS mount then root squash should be disabled as mergerfs needs to be able to have elevated privileges to do what it does.
If you are exporting mergerfs over NFS then it is not really necessary.
See the section on remote filesystems.
Does inotify and fanotify work?
Yes. You can test by using inotifywait or inotifywatch.
However, you can not get notifications for events that occur outside of the mergerfs mount. For instance if you are doing out-of-band changes it is not possible to get those events forwarded through mergerfs. FUSE offers no mechanism to publish events and even if it did it would require somewhat expensive inotify or fanotify watches on all branches.
Most software which has the ability to actively monitor a filesystem
(such as Plex, Emby, Jellyfin, Airsonic, etc.) are using inotify or
fanotify.
If you must add content out-of-band the only way to get real-time
updates (via inotify or fanotify) is to add the underlying branches to
the software rather than using the mergerfs mount. An alternative is
to enable regular library scanning. Plex, for instance, has "Scan my
library periodically". Additionally, if you are using software such as
Radarr, Sonarr, or Lidarr you can configure it to trigger library
updates in a number of services. This can be found under Settings > Connect.