Mount root error / New device numbering?

Jeremy Chadwick freebsd at
Fri May 14 03:06:34 UTC 2010

On Thu, May 13, 2010 at 11:00:38PM -0300, Fred Souza wrote:
> I give up and reinstall (that first install had given me quite a
> headache with incorrect drive geometry [that I had to fix with a lot
> of research to get to TestDisk and GAG], so I thought it was best to
> just start fresh). I do the same procedure this time, but paying extra
> attention to any details I could have overlooked before. One of them
> was to make a kernel (-STABLE) out of a renamed copy of GENERIC (no
> options added or removed). I also decided on doing the remaining steps
> listed on /usr/src/UPDATING before rebooting; I thought the drive
> numbering difference could be related to something in userland that
> was missing when booting the -STABLE kernel with -RELEASE userland.
> ...
> And I got the same mount root error message, and again it shows the
> drives as ad10 and ad16 instead of ad8 and ad14. The difference is
> that this time I did not try to update /etc/fstab before resorting to
> this list (I had been browsing it for the past 3 days trying to find
> any hints on this, as well as reading /usr/src/UPDATING in full
> again). I can get the system to boot normally if I unload the -STABLE
> kernel and load the -RELEASE one. But I can't figure out for the life
> of me why does -STABLE shift my drive numbers around.

There is probably an ata(4) device layer change which either fixes (yes
really), breaks (possibly), or enhances (likely) support for your ATA or
SATA controller.  This is pretty much how the ata(4) layer has behaved
for years upon years -- that's just how it goes.  If this is your first
time encountering it, congratulations.  :-)  The device names *should
not* change on you once you stick with that kernel; it just indicates
something changed between -RELEASE and -STABLE.

I'd recommend booting/trying an actual 8.0-STABLE snapshot image from

This will allow you to boot and install 8.0-STABLE on your system.  You
should see devices ad10 and ad16 there as well.  It would at least save
you the pain of installing the kernel, rebooting, and finding you have
to manually deal with /etc/fstab changes and so on.  Give this a shot

It also might help in debugging the "stray IRQ" problem you see (it
would be useful to know what's sitting on IRQ 21; it may be an unused
device in your BIOS which you can disable there, or try to find a
FreeBSD driver for the device which can attach to the IRQ).

| Jeremy Chadwick                                   jdc at |
| Parodius Networking              |
| UNIX Systems Administrator                  Mountain View, CA, USA |
| Making life hard for others since 1977.              PGP: 4BD6C0CB |

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