While working through the Cloud-Init at https://pve.proxmox.com/wiki/Cloud-Init_Support to create a Template on my PVE7 system that is using BTRFS storage I get the following error:
$ sudo qm set 100 --scsihw virtio-scsi-pci --scsi0 local-btrfs:100/vm-100-disk-0.raw
update VM 100: -scsi0...