So the best way to backup your VM disks will be either setting up a sync job with snapshots of your zvols or manually using zfs send
. I won't go in depth on the command and I'm no expert but if you google "zfs send tar" you will find some great examples of how to "send" a snapshot to an archive file like a .tar or .gz that you can save to a shared folder and just copy it off to wherever. Just make note of the reverse process too!