Jul 28 13:36:09 pve zfs[1429]: cannot mount '/zfs-pool': directory is not empty Jul 28 13:36:09 pve systemd[1]: zfs-mount.service: Main process exited, code=exited, status=1/FAILURE Jul 28 13:36:09 pve systemd[1]: zfs-mount.service: Failed with result 'exit-code'. Jul 28 ...
HDDs should be defragmented for better performance, so it might do that. But defragmenting a CoW HDD pool or a SSD won't help anything but will just cause massive wear so it will fail sooner. Would be really bad if the guest OS tried to defrag the virtual HDD that sits ontop of ...