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Date:      Tue, 7 Jan 2003 16:03:08 +0100 (CET)
From:      Soeren Schmidt <sos@spider.deepcore.dk>
To:        eculp@encontacto.net
Cc:        "current@FreeBSD.ORG" <current@FreeBSD.ORG>
Subject:   Re: mirrored root fs?
Message-ID:  <200301071503.h07F38hS044177@spider.deepcore.dk>
In-Reply-To: <1041951264.3e1aea2012592@Mail.EnContacto.Net>

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It seems eculp@encontacto.net wrote:
> Søren,
> 
> This is a real temptation.  Let me be sure that I'm understanding 
> correctly.  I have an old machine, but running today's current, with only 
> one disk, ad0. Could I do the following?
> 
>   o- Add ad2
>   o- run atacontrol create RAID1 ad0 ad2 source ad0
>   o- change ad0s1a to ar0s1a through ad0s1f to ar0s1f in fstab
>   o- reboot and enjoy my new mirror.

Exactly, modulo the "source ad0" bit which is not in atacontrol (yet),
it will always the the first disk (ad0 here) in the mirror as the
master to make the mirror from.

> If ar0 were to die, I would just take it out connect ar2 and boot as ?
> I could then do the same with a new mirror, I suppose?

If one of the disks die, you can boot on the degraded mirror, one
caveat is that your BIOS might not want to boot from "ad2" just
from "ad0", if thats the case swap the drives, and boot...
Then when you are up, atacontrol detach the failed device, swap
it with a new one, atacontrol attach, atacontrol rebuild, voila...

Another way is to boot the degraded mirror, then when its up you
do a atacontrol delete to get rid of the mirror, remember to change
your fstab back to adX instead of arX, and reboot...

> If I'm understanding correctly, I could use any disk > ad0 as the mirror.
> Is that correct?  

Yes, as it is currently it must be on another non-RAID controller, or
the BIOS on there will get mighty confused only having part of a
RAID config on it :)

> One last question, what prompted you to preceed the patch with 
> "For those that are brave enough to play with this", where could
> it come back and bit me? :-)

Doing "stuff" to your root filesystems is always dangerous, so you
have been warned :)

-Søren

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