How to predict drive number change for 7.3->8.1 upgrade?

[Marat N.Afanasyev]

Michael Sperber wrote:
>
> I just upgraded my desktop system from 7.3 to 8.1, and the main hard
> drive, which was /dev/ad6 before is now /dev/ad10.  Consequently, the
> initial boot failed when trying to mount the root file system from ad6.
>
> The desktop system is now fixed, but I also have a rented server with
> only a serial console, and I worry that the upgrade is going to leave me
> with a dead machine.  Is there any way to predict how the drive number
> changes?  (Why does it change at all?)  If so, what's the proper way to
> tell the system the initial root device *before* rebooting?
>
you may try to label your slices/labels and mount /dev/label/root 
instead of /dev/adXsYa

see
man 8 glabel

-- 
SY, Marat