After buying a new Apple TV last year I have been trying to use the Plex App for all my media needs outside of Netflix. I run the Plex Media Server on an old Mac with a very small SSD and lots of External HD space which contains my media. Because of this I needed to do some tweaks to get it to work.

On OS X, Plex keeps all its metadata in ~/Library/Application Support/Plex Media Server. I shouldn’t have been surprised when shortly after firing it up I got a low disk space warning as the downloaded metadata for my library quickly ate through what little space I had remaining on the boot volume. Fortunately this was quite straightforward to fix:

1. Shutdown Plex Media Server
2. Move ~/Library/Application Support/Plex Media Server into a different location with more available space (in my case /Volumes/Media which is my External HD)
3. From the terminal run the following command: ln -s "/Volumes/Media/Plex Media Server/" "~/Library/Application Support/Plex Media Server"
4. Relaunch Plex Media Server

Ensure you substitute /Volumes/Media/Plex Media Server/ with the correct location you moved it to, while keeping the second path (~/Library...) exactly the same. These steps replace the original folder with a symbolic link to the external drive. When Plex attempts to access data in the directory, OS X will transparently point it to the External Drive instead without using up any precious SSD space.

All was well and I was using this setup for several months until I tried to play a 1080p file which needed transcoding. Whenever I selected the file Plex would briefly attempt to load before returning back to the menus. Looking in the Plex Server dashboard I could see that there was no transcoding in progress but no other errors. Checking for any settings related to transcoding it seemed like it would put transcoded files in the external drive so I didn’t think that was the issue. I figured the Mac simply wasn’t powerful enough to transcode the video and thought no more of it.

Until last night! I was bothered by the fact that it simply did nothing. If the machine wasn’t powerful enough I would have expected buffering problems and even manual transcoding in advance wasn’t working. I enabled Debug logging under Settings -> Server -> General and took a look in ~/Library/Logs/Plex Media Server.log and immediately spotted the problem:

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Mar 11, 2016 18:40:46 [0x70000021d000] WARN - Low disk space: 7351296544 bytes
source file, 31495843840 bytes capacity, 4046225408 bytes available on
/Users/argon/Library/Caches/PlexMediaServer/Transcode/Sessions

The transcoding was happening outside of the Application Support directory and instead using another path on the SSD so there simply wasn’t enough available space. I used the same steps above to move the Transcode directory to the external drive as well and now transcoding works perfectly.

These were the steps I used to fix the transcoding as well:

1. $ rm -rf ~/Library/Caches/PlexMediaServer/Transcode
2. $ mkdir "/Volumes/Media/Plex Media Server/Transcode"
3. $ ln -s "/Volumes/Media/Plex Media Server/Transcode/" "~/Library/Caches/PlexMediaServer/Transcode"

With these and the steps above Plex should work perfectly on your Mac, Transcoding and all.