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Date: Sat, 30 Nov 2013 14:17:39 -0700 (MST)
From: Warren Block <wblock@wonkity.com>
To: "Mike." <the.lists@mgm51.com>
Subject: Re: gmirror, gpart and MBR vs GPT in the Handbook
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On Sat, 30 Nov 2013, Mike. wrote:

> The Handbook page about creating a gmirror array
> ( http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/geom-mirror.html )
> has the command:
>
> 	gpart create -s MBR mirror/gm0
>
> I've read elsewhere in the handbook that GPT is preferrable to
> the older and less versatile MBR scheme.

Mostly, it is.

> Is there a specific reason why MBR was used in the Handbook
> example for creating a mirror, instead of GPT?

Yes, there was, see the last paragraph of the Metadata Issues 
subsection, 
http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/geom-mirror.html#geom-mirror-metadata

> Or was it just a preference of the person who wrote that Handbook 
> page?

That was me, and I would much prefer GPT.  However, whole-disk gmirror 
metadata and the GPT backup table conflict.