@support, I have a regular backup that runs of my home directory on Mac OSX. I noticed today that I had a backup that had been running since Feb 2nd - and also that my backup drive was almost full.
Digging into this, it appears that the behavior of the ~/Library/RoonMounts directory has changed. I previously hadn’t noticed that this location contained a copy of my mounted music folder. This wasn’t an issue with Roon 1.2 as the total size of my music is only a few hundred Gb so didn’t impact my backup too much. With Roon 1.3 however, the entire disk containing the music - and also other media files (video mainly) has been mounted at this location - so my backup was trying to copy terabytes of data.
I can resolve this by excluding ~/Library/RoonMounts from my backup - however I thought you should know in case other people have the same issue.