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Date: Wed, 1 Oct 2008 08:41:18 +0200 (CEST)
From: Wojciech Puchar <wojtek@wojtek.tensor.gdynia.pl>
To: Andrew Falanga <af300wsm@gmail.com>
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Cc: "freebsd-questions@freebsd.org" <freebsd-questions@freebsd.org>
Subject: Re: Setting up gmirror
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> Hi,
>
> I've just finished setting up a new web server, and if I get my DNS
> stuff correct hopefully an e-mail server too, for my church.
> Originally, the intention was to use RAID1 on the MOBO.  However, the

do not ever use "hardware" RAID0/1/10 on motherboard.
first it's not hardware, it's purely software, second there is nothing to 
be accelerated by hardware on RAID0/1/10.

use gmirror/gstripe/gconcat everywhere.

> make any mention of gmirror(8).  It seems like gmirror is rather easy

gmirror is easy to set up and works excellent.
> Identical drive models so their sizes are the same.  Is this the
> command, from gmirror(8), the one I'll want to use?
>
>     Create a mirror on disk with valid data (note that the last sector of the
>     disk will be overwritten).  Add another disk to this mirror, so it will
>     be synchronized with existing disk:
>
> 	   gmirror label -v -b round-robin data da0

add -s <very large value> like -s 1048576 to prevent splitting one request 
on 2 disks.

except this - all right.

> 	   gmirror insert data da1
> Though in my case, da0 and da1 will be ad4 and ad5.  This seems to be
> the one I'm looking for, I'm just scared of wiping out more than I
> bargain for.

assuming you already have system on say ad4, make gmirror on ad5, copy 
everything, make sure it's bootable (bsdlabel -B ...), boot from it, if 
all works, add ad4 to the mirror effectively overwriting things.

add in loader.conf

vfs.root.mountfrom="ufs:mirror/dataa" - assuming your system is on 
partition a of your mirror.


HINT - you DO NOT have to mirror whole drive. you may mirror a 
partition(s), living some of them unmirrored.