From owner-freebsd-geom@FreeBSD.ORG  Wed Aug 16 11:37:47 2006
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Date: Wed, 16 Aug 2006 13:37:43 +0200
From: Danny Carroll <danny@dannysplace.net>
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Subject: Mirror MBR?
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Hello all.

I had a question about gmirror.  I am using Ralf S Engelschall's
mirroring solution at http://people.freebsd.org/~rse/mirror/

I used solution one, since I am sure that I will never be using any
different disks.  It's a pizzabox server, and I don't expect data growth
so the current disks are fine.

My main question is about the MBR. I dont see anywhere in the doc where
I should put a new boot record on the disk after doing:

dd if=/dev/zero of=/dev/ad0 bs=512 count=79

Does this mean that the MBR from the mirror gets put onto this first disk?

I ask because, I need to know what should happen when I need to replace
a disk.

I know that after replacing the disk I should probably have to do
something like this: (Assume ad0 is the new disk)

gmirror configure -a gm0
gmirror insert gm0 /dev/ad1

But does that guarantee me that if ad0 fails, then I still have a
bootable system (assuming bios knows to boot of ad1).

Thanks for your time.