> Hi Fab.
> 
> 1. Will it run without the "trick"

The system ? I don't know, but I think init can execute everything,
interactively or not...

> 2. Is the device there at all?

Yes.

> 3. Is the FS on the device fat ?

Yes.

The device is a simple FAT usb hard drive I mount everyday.
disklabel shows the sd0e with MSDOS filesystem on it.

I have to do some correction, the message is "invalid argument" and not
the previous one, hope this helps.

Fabien Devaux.