create raid1 on a installed system

[Rashkae]

Asif Iqbal wrote:

> 
> http://wiki.xtronics.com/index.php/Raid uses (uses mkinitrd)
> 

this article is a bad resource.  Those tricks to make initrd work with
SATA might have been needed on some old versions of Debian, but
certainly not now.

And unless you want to have to build your own initrd every time
automatic updates run, then the idea to define the raid array in
mdadm.conf doesn't make much sense.  Just let mdadm -a do it's thing,
like magic.