A media server stores artwork and thumbnails for everything, including deleted films

A media server does not only index your files. It downloads artwork, builds preview thumbnails and keeps a database of everything it has ever seen, and on a large library that metadata is measured in gigabytes.

Where it is on Windows

$plex = "$env:LOCALAPPDATA\Plex Media Server"
Get-ChildItem $plex -Directory -EA SilentlyContinue | ForEach-Object {
  $s = (Get-ChildItem $_.FullName -Recurse -Force -File -EA SilentlyContinue | Measure-Object Length -Sum).Sum
  [PSCustomObject]@{ MB = [math]::Round($s/1MB); Folder = $_.Name }
} | Sort-Object MB -Descending

Video thumbnails are optional and expensive

The setting that generates preview thumbnails for scrubbing creates 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.

Transcoding on Windows

The transcoder writes temporary files while converting a stream, and its folder defaults to the system drive. On a server that transcodes regularly, pointing it at a second drive in Settings, Transcoder keeps that traffic off C entirely.

Optimised versions

Converted copies made for streaming to phones are full second copies of the media, stored with the library rather than the metadata. One optimised season is larger than all the artwork put together, which is why they are worth checking separately.

Cleaning up properly

The server has scheduled maintenance tasks for cleaning old bundles and emptying trash, which update the database as they go. That is safer and more thorough than deleting folders, and the database itself should never be removed: it holds watch history and ratings that nothing recreates.