Are my Plex libraries etc backed up to the Plex server? Do I need to back up locally as well?

Hello I am using Plex on an iMac with OS X El Capitan v 10.11.5.
I back up using Time Machine to an external hard drive.
However the drive has become full.
Does the Plex server automatically back up all my libraries in both original and optimised versions?
If so doe I need to continue to back up Plex libraries and how would i recover my files from Plex?
I've looked through various threads but can't see anything relevant to Apple users.
All help/advice really welcome.