Comment # 2 on bug 899368 from Arvin Schnell

The setup is currently not supported.

There is already a feature request (#316251, unfortunately not public)
dealing with this. The feature request deals only with using whole disks
for e.g. btrfs but not with booting from such a disk. In case you also
want that (I assume "install OS" means that), please open a feature
request.