Lost MBR/wrong disk geometry

[Erik Norgaard]

Hi,

It appears that I have screwed my disk (60GB) thoroughly. I had used the 
sample install.cfg for sysinstall but it has "partition=exclusive" and 
not "all". I did

   dd if=/dev/zero of=/dev/ad0 count=1k

as explained in the faq, and the exclusive partioning was gone.

I can run sysinstall, slice up the disk and install stuff. But on reboot 
the system doesn't find a usefull mbr.

I can boot up a rescue disk, mount the partitions, read data stored and 
use any programs installed. But I can't recover or create a new mbr with

   dd if=/boot/mbr of=/dev/ad0

or with /boot/boot0, or use fdisk to manually set slices and active 
slice, run sysinstall and choose a bootmanager or similar.

Please, how to I get back an mbr and a working partition table?

Thanks!

Cheers, Erik

PS:

When sysinstall ran first, it complained about a wrong geometry, 
116280/16/63 and tried to rewrite it to 7296/255/63. The bios reports 
28728/16/255 and the label on the disk sais 16383/16/63.

Accepting the geometry from sysinstall would make the installation 
complete but on reboot the system booted up with the old geometry.

On my laptop my disk (40GB) has geometry 77520/16/63 so I hacked up 
sysinstall to accept the geomtry (a simple change). With this I can 
slice up the disk and install the system.

I don't know if this is right, but from my current state, I'd say that 
the only thing is the mbr not being written correctly to the disk...

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