Thanks very much for the reply (and on discord!). You pointed me to where the issue was - I think. The vdisk1.img file is on disk1, which is a ZFS file system with a domains dataset, and a UbuntuTest dataset. When the VM configuration points to the vdisk via /mnt/user/domains/UbuntuTest/vdisk1.img the snapshots are not created (because user is not a zfs dataset/pool). When the VM configuration points to the vdisk via /mnt/disk1/domains/UbuntuTest/vdisk1.img the snapshots are created (because disk1 is a zfs pool). So I think it was my bad referring to the VM via the user share, instead of the disk directly. Please let me know if this is the correct reasoning. Thank you for the help!