In case some reader stumbling over this might not know, btrfs snapshots operate in a copy on write fashion, so if two older snapshots reference the same unchanged file this file will not actually be stored twice for the snapshots but only once, and if the file in the current filesystem has not changed from when the snapshots were taken not even a single back-up copy exists. This copy will be automatically created once a process starts changing the file, and as far as I know there will only be a single back-up.
Now if the file changed between the snapshots there will be multiple copiesā¦
A consequence of this is that it is unintuitive how much ādisk-spaceā is recovered from deleting snapshots and how much space deletion of an arbitrary snapshot recovers⦠that said keeping all snapshots for ever will not work, but I would make snapshot deletion partially dependent on the amount of free spaceā¦