Unable to mount the root fs on stable/8 r264339, GENERIC kernel, with MBR, FreeBSD slice, and UFS volume labels

[Warren Block]

On Fri, 11 Apr 2014, Chris H wrote:
>>
>> There I first wiped the harddrive clean, by booting from the
>> 8.0-RELEASE dvd1, ran dd if=/dev/zero of=/dev/ad0 bs=128M, before I
>> installed 8.0-RELEASE. I then transferred an up-to-date working copy
>> of stable/8 to the spare system. Next, I compiled world and the
>> GENERIC kernel, without any hassle. I performed make installkernel and
>> rebooted.
>>
>> The boot loader managed its way through the maze, read /etc/fstab and
>> found the entry for the root filesystem. The new GENERIC kernel,
>> however, simply can't understand what to do with:
>>
>> vfs.root.mountfrom="ufs:/dev/ufs/root"
>> vfs.root.mountfrom.options="rw"
>>
>> as presented by the boot loader. Mind you, the boot loader hasn't been
>> replaced yet. Maybe that's the whole issue, however weird it sounds.
>> /boot/loader.conf is empty btw.
>>
>> I'm doing a similar attempt in VirtualBox at home as I write this.
>> There I began with 8.4-RELEASE, and are currently compiling stable/8
>> r264351.
>>
>> I'll later try in VBox, 8.4-R -> stable/8 with GPT + UFS, using GPT
>> labels, just to rule out UFS labels.
> Looks to me like you're suffering a mix of MBR + GPT. It /appears/ to
> be expecting one of them, but getting the other. Did you install the
> bootcode, or update it? Was it consistent with your choice of
> schemes (GPT v MBR)? Well. Looks like you're on the right track. As
> far as I can see. Good luck. :)

My first guess would be missing bootcode in the BSDlabel slice.  But I 
may have missed that when I missed earlier parts of this thread.

In general, use GPT unless there is some reason to avoid it. 
http://www.wonkity.com/~wblock/docs/html/disksetup.html shows both GPT 
and MBR/BSDlabel setup.