I'm not sure you can do it that way as dos doesn't see external devices. I had to hook up my firewire hd as slave to 'c' master and formatted etc there.
BTW the prob of external hd not being seen could be the jumper settings.
HP Envy x2 review: Hands-on
How Sketch and InVision have revolutionised our design workflow
The best tech gifts for Christmas 2017
Les meilleurs jeux de société (2017)