@anarceus
I would have \two\ dishwashers so I can leave clean dishes in one and transfer them directly to the dirty one as I use them.
A zvol’s used can exceed what the guest believes it is using, sometimes dramatically. ...which netbsd does not support, unless ZFS somehow can without fstrim (which wouldn't surprise me since ZFS seems happy to implement its own things).
The fix is discard/TRIM from the consumer: