freebsd stable - Aug 2008 - Swapping boot disks and getting mountroot>

I have a system running FBSD 6.2 release (if I remember correctly) that 
is running on a Sunfire X2100.  The disk boots fine there and I seem to 
be able to move it to other X2100's.  The problem is that I need to move 
it to a Sunfire X2200.  When I move it to the X2200 I get a mountroot> 
prompt and the keyboard freezes up.

I notice that it finds the device ad4 but then it tries to mount root 
from /dev/ad6s1a.  I've edited the fstab to have it look for ad4s1a but 
it still won't boot.  Anyone have any pointers or ideas?

Thanks,

Lisa B.

> I notice that it finds the device ad4 but then it tries to mount root from
> /dev/ad6s1a.  I've edited the fstab to have it look for ad4s1a but it
still
> won't boot.  Anyone have any pointers or ideas?
Have you tried interrupting the boot sequence and setting new
values for the `rootdev' and `root_disk_unit' loader variables?
The loader(8) manual page has more information.

Koshy