can't mount root during freebsd-update 7.0 -> 8.1 on amd64

[David DEMELIER]

2010/12/5  <joost at jodocus.org>:
> Hi
>
> I'm trying to upgrade a amd64 box from 7.0-RELEASE to 8.1-RELEASE with
> freebsd-update. After the first reboot the 8.1R GENERIC kernel loads (I'm
> using a custom kernel, so at this point the generic kernel is loaded
> manually)
> It then claims it can't mount /
>
> One thing that's odd is that instead of finding ad4s1a it finds ad4a. Same
> for the other filesystems. It however can't find init on this device.
>
> Did I miss something important in src/UPDATING?
>
>
> Thanks
>
>
> Joost Bekkers
>
>
>
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Here : http://ivoras.sharanet.org/freebsd/freebsd8.html

GEOM_PART becomes the default slicer

Status: Committed to -CURRENT
Will appear in 8.0: sure
Author: Marcel Moolenaar & others
Web: commit message

GEOM_PART (gpart) is a new GEOM partition class (slicer) and utility
that rolls up support for many partitioning formats (MBR, BSD, GPT
etc.) into a single code base.

NOTE: Caveat when upgrading! GEOM_PART might interpret existing
partition tables (especially if many operating systems are present -
multi boot) differently than the previous classes. Your devices might
get renamed.

NOTE: Some old utilities like bsdlabel may not work if the kernel
doesn't include GEOM_BSD and other old slicer classes. In other words,
bsdlabel et al don't work with GEOM_PART.

Maybe you're encountering this trouble right now. what I would advise
you is using labels. Please do the following :

tunefs -L root /dev/ad4a
tunefs -L var /dev/ad4e (assuming it's e on your system ?)
and for usr, tmp, etc ...

>From a fixit environment. then edit your /etc/fstab and place
/dev/ufs/root /dev/ufs/var instead of hardcoding the device node.

Cheers,

-- 
Demelier David