A media server stores artwork and thumbnails for everything, including what you deleted
Plex builds a metadata library that grows with every item scanned. Where it lives, what generating thumbnails costs, and how to trim it.
A media server does not only index your files, it downloads artwork, builds thumbnails and keeps a database of everything it has ever seen. On a large library, that metadata is measured in gigabytes and it does not shrink when the media does.
Where it is
du -sh ~/Library/Application\ Support/Plex\ Media\ Server 2>/dev/null
du -sh ~/Library/Application\ Support/Plex\ Media\ Server/* 2>/dev/null \
| sort -h | tail -8| Folder | What it is | Safe to clear |
|---|---|---|
Metadata | Artwork, posters, thumbnails | Yes, redownloaded |
Media | Generated video thumbnails | Yes, and it is often the largest |
Plug-in Support/Databases | The library database | No, this is watch state and settings |
Cache | Transcoding and general cache | Yes |
Logs | Diagnostics | Yes |
Video thumbnails are optional and expensive
The setting that generates preview thumbnails for scrubbing produces an image every few seconds for every video in the library. It is genuinely useful and it is the single biggest contributor to metadata size. Turning it off and clearing the generated files is the largest available win if you do not use scrubbing previews.
Optimised versions
Optimised or converted copies made for streaming to phones are full second copies of the media, stored inside the library folders rather than with the metadata. They are worth checking separately, because one optimised season is larger than all the artwork put together.
Cleaning up bundles for deleted media
The server has maintenance tasks that remove metadata for items no longer present, usually under settings for scheduled tasks, including one to clean old bundles and one to empty trash. Running those is safer and more thorough than deleting folders, since the database is updated at the same time.
If the media itself is what fills the drive, that is a different question with a clear answer, and moving files to an external drive covers doing it in a way the server can still find.
Common questions
Where does Plex store metadata on a Mac?
In ~/Library/Application Support/Plex Media Server, with separate folders for metadata, generated media thumbnails, databases, cache and logs.
Can I delete Plex metadata to free space?
Artwork, thumbnails and cache can be cleared and are downloaded or regenerated again. The databases folder holds watch history and settings and should never be deleted.
Why is Plex metadata so large?
Usually generated video preview thumbnails, which create an image every few seconds for every video. Turning that setting off and clearing the generated files is the biggest single reduction available.
What are optimised versions in Plex?
Converted copies of your media made for easier streaming, stored as full second copies of the files. They are separate from metadata and are frequently larger than everything else combined.