Merci, Stéphane!
So I can truncate up and down as desired, it is up to me to keep it under the physical max? Similar to thin provisioned LVM?
and are these steps necessary after truncating? I am drawing these steps from this post
sudo zpool set autoexpand=on default
sudo zpool online -e default /var/lib/lxd/disks/default.img
sudo zpool set autoexpand=off default
Also, what is the default max per volume? I have some with hundreds of GB, and the smallest one is just shy of 50GB