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Date: Wed, 30 Jan 2013 07:06:45 -0700 (MST)
From: Warren Block <wblock@wonkity.com>
To: Artem Kuchin <matrix@itlegion.ru>
Subject: Re: Software raid VS hardware raid
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On Wed, 30 Jan 2013, Artem Kuchin wrote:

>
> 30.01.2013 1:01, Warren Block:
>> On Tue, 29 Jan 2013, Artem Kuchin wrote:
>> 
>>> 
>>> 29.01.2013 18:57, Warren Block:
>>>> On Tue, 29 Jan 2013, Artem Kuchin wrote:
>>>> 
>>>> The Handbook chapter on gmirror talks about the problems with GPT and 
>>>> GEOM metadata.  In short: right now, they conflict. It's possible to 
>>>> mirror GPT partitions, but be aware that if you mirror more than one 
>>>> partition on a drive, a rebuild after replacing a drive could thrash the 
>>>> heads as mirrors are rebuilt simultaneously.
>>>> 
>>>> http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/geom-mirror.html 
>>>> 
>>> 
>>> So,
>>> gmirror+GPT=conflict on last sector
>>> GPT+gmirror = hardrive head kill
>>> 
>>> nice...
>>> 
>>> So, for no more than 2TB disks the best way to go is GMIRROR of the drive 
>>> +PARTITION on top of it?
>> 
>> GPT partitions should work, just limit it to one mirrored partition per 
>> drive.
>
> Please, clarify what you mean here.

If only one GPT partition on a drive is mirrored with another GPT 
partition on another drive, head contention never comes up.  There is 
only one mirror.

It does nearly eliminate the usefulness of GPT partitioning.