My installation is a few months old, maybe 4 months.
Decided to run the first defrag yesterday, but before I checked the disk usage, it was about 21GB.
After the defrag, noticed that the space used increased to 26GB.
Since the info above is specifically saying about “break” links, I decided to test my system and everything was working perfectly.
In my opinion, which could be premature and with little knowledge about the technical stuff, is that these links that “break” are only for the snapshots, but they still work, they just consume more space after the defrag.
Decided then to erase my snapshots and my system is now using 16GB of space…
Since then I decided not to use it anymore…
Also, keep in mind that if you monitor the disk usage by typing: iotop -a, you will see that btrfs is writing to the disk more often with the autodefrag option.
If you use the same options on all your subvolumes, you should use those options there as well. It may or may not make much difference depending on how you use that mountpoint.
Many of the btrfs options actually apply to all subvolumes of the same filesystem. For example, if you look at findmnt /btrfs you will probably see that compression and some other options are being applied to it even though you didn’t specify them explicitly.
If you want to explicitly mount the root you should probably use subvolid=5. What you are currently doing is mounting the default subvolume which is currently set to /. If you ever changed the default subvolume, what you have mounted there would change too.