Media Metadata View

/mnt/media is an OverlayFS merge of the media library: the RAID6 array below, a directory on the NVMe above. It exists so Jellyfin can write Kodi-format sidecars (movie.nfo, tvshow.nfo, episode.nfo, artwork) that Plex can read. Sidecar metadata is only useful sitting next to the media file, and the array is read-only and slow — so the bytes stay there and the writes land on SSD. One tree to both servers, one copy of the media.

Shape

Item	Value
Lower layer	`/mnt/entropy` — the RAID6 array, source of truth, never written
Upper layer	`/var/lib/media-meta/upper` — NVMe; every write lands here
Work dir	`/var/lib/media-meta/work` — overlayfs internals, same filesystem
Mount point	`/mnt/media`, unit `mnt-media.mount` (`WantedBy=local-fs.target`)
Repo source	`dankserver/host/systemd/mnt-media.mount` — host copy is generated state
Installer	`scripts/media-view.sh` — `plan` / `install` / `verify` / `status` / `reap`
Written by	Jellyfin only (Plex binds read-only); nothing else in the fleet touches it

Both consumers guard the view with UnitConfigItem=ConditionPathIsMountPoint=/mnt/media, and scripts/deploy.sh dankserver --service jellyfin|plex calls media-view.sh install + verify before it restarts either container.

Consumer	Bind	Mode	Why that path
Jellyfin	`/mnt/media:/data`	rw	It is the metadata writer; its sidecars become SSD bytes
Plex	`/mnt/media:/mnt/entropy`	ro	Every path in the PMS database was recorded as `/mnt/entropy/...`; only the HOST side of the bind moved, so its database still resolves

Putting the sidecars inside Plex's reach is not the same as making Plex use them: a library parses .nfo only with its Local media information agent enabled, and this change touches no library setting.

Commands

scripts/media-view.sh plan              # print the resolved shape, touch nothing
sudo scripts/media-view.sh install      # create dirs, install the unit, mount, enable
scripts/media-view.sh verify            # is /mnt/media really the overlay? (deploy gate)
scripts/media-view.sh status            # mount options + upper-layer size/file count
scripts/media-view.sh reap              # list ghost metadata (media moved, sidecars left)
sudo scripts/media-view.sh reap --apply # move ghosts to the SSD trash, never delete

--upper-base DIR and --lower DIR relocate the layers; the defaults are the host values above.

Laws

The upper layer must sit on non-rotational storage. install and verify refuse via lsblk -dno ROTA if the upper base lives on the array: an overlay whose upper is the spinners is the original problem with extra steps, and it silently turns every metadata write back into a seek.
Never mount the view over an unmounted lower. RequiresMountsFor=/mnt/entropy plus the container ConditionPathIsMountPoint guards: an empty lowerdir presents an empty library as truth, and a media scan would then clear the database of everything.
Never delete through /mnt/media. A delete writes an overlayfs whiteout (.wh.<name>) in the upper layer, which hides the array's copy without removing it — the file reappears the moment the view is unmounted, and the upper layer now carries a landmine. Deletions belong on the raw path (/mnt/entropy), which the relayout tool already treats as the only writer. reap refuses to remove whiteouts and only warns about them.
A relayout must be followed by reap. Renames happen on the raw path, so sidecars the view already wrote stay at the old coordinates: a ghost folder the servers browse and find nothing in. reap lists upper-layer directories with no counterpart below and moves them (with their subtree) into a dated .AGENTTRASH/ under the SSD base. It is recursive and file-safe: a sidecar that exists only above is normal, so only directories are candidates.
File-watcher events do not cross the overlay. Plex's NFO agent and Jellyfin's real-time monitor see inotify events for writes that land in the upper layer, not for changes on the array underneath. After any relayout or externally-written metadata, trigger a library refresh — see Media Relayout for the refresh procedure.

Failure signatures

Symptom	Meaning
`jellyfin.service` / `plex.service` show `ConditionPathIsMountPoint=... was not met` and stay inactive	`/mnt/media` is not mounted. Do not start them anyway: `scripts/media-view.sh install`, then `verify`.
Jellyfin log: `Read-only file system : '/data/Movies/…/movie.nfo'`	The container is binding the raw array, not the view — the quadlet drifted back or the view is gone. `media-view.sh status`.
A folder appears in a media server with artwork/`.nfo` but no video	Ghost metadata from a relayout. `media-view.sh reap`.
`verify` prints `refused: /mnt/media is not a mountpoint`	Someone made a plain directory there. That is the fail-closed guard working; remove it and install.

Rollback

Revert the commit that pointed the two quadlets at the view and re-deploy both services — they bind /mnt/entropy read-only again, which is the pre-view shape. The NVMe upper layer can stay: nothing reads it once the binds are back, and it holds no state either server needs. Removing the mount alone (systemctl stop mnt-media.mount) is safe while no container binds it, and the array is never modified by any of this.

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