Normally you are not allowed to use any 'full' fixed disk devices.
mkdosfs
will complain and tell you that it refuses to work. This is different
when usind MO disks. One doesn't always need partitions on MO disks.
The filesytem can go directly to the whole disk. Under other OSes
this is known as the 'superfloppy' format.
This switch will force
mkdosfs
to work properly.