Re-installing bootmanager

[Guy Van Sanden]

Hello

I tried to follow some suggestions I got on this list to get my
self-made mirror-disk to boot.

The tip was the use /stand/sysinstall - config - fdisk - disklabel and
let it install a bootmanager.
I tried to do this, however it did not write my slices to the disk.
(no errors or anything, it just didn't write it).

I used fdisk from the console, and that worked.
However, now I don't have the disk bootable.

The device is /dev/ad1, the root filesystem is on /dev/ad1s1a
The disk is a backup/mirror, so it should only be booted as a
replacement for my main disk on /dev/ad0.

How do I get it bootable now? (so installing bootmanager and letting it
to boot the kernel on the s1a partition.

Kind regards

Guy