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Date: Sun, 25 Jun 2006 14:14:03 -0400
From: Mike Jakubik <mikej@rogers.com>
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To: Matthew Seaman <m.seaman@infracaninophile.co.uk>
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Cc: =?ISO-8859-1?Q?V=E1clav_Haisman?= <V.Haisman@sh.cvut.cz>,
	freebsd-stable@freebsd.org
Subject: Re: Setting up GEOM mirror
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Matthew Seaman wrote:
> Václav Haisman wrote:
>   
>> Hi,
>> I want to set up GEOM mirror of whole existing partitioned 250G disk.
>> The procedure described at <http://people.freebsd.org/~rse/mirror/>
>> seems to be rather long/complicated. I thought about using this:
>>
>> # Boot into single user, then...
>> # First change fstab.
>> cp -p /etc/fstab /etc/fstab.orig
>> sed -e 's/dev\/ad0/dev\/mirror\/gm0/g' </etc/fstab.orig >/etc/fstab
>> # Then create the mirror.
>> gmirror label -v -b split -s 2048 mymirror ad0
>> gmirror insert -h mymirror ad2
>> # Reboot into the new World order.
>> shutdown -r now
>>
>> Will this work or is it wrong? I appreciate any comment to this.
>>     
>
> http://www.onlamp.com/pub/a/bsd/2005/11/10/FreeBSD_Basics.html
>   

The problem with these instructions is that they don't take in to 
account the last sector. You may very well end up writing the metadata 
on the file system.