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Date:      Mon, 11 Mar 2013 11:09:22 -0700
From:      Cody Ritts <cr@caltel.com>
To:        freebsd-fs@freebsd.org
Subject:   Re: Aligning MBR for ZFS boot help
Message-ID:  <513E1DD2.7030609@caltel.com>
In-Reply-To: <513D0E90.5090105@platinum.linux.pl>
References:  <513C1629.50501@caltel.com> <513D0E90.5090105@platinum.linux.pl>

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On 3/10/13 3:52 PM, Adam Nowacki wrote:
> I don't think zfsboot is aware of BSD disklabel (offsets other than 0
> won't boot). Is there any reason you are using BSD disklabel and not two
> partition MBR?

The reason is because every example I saw used labels.
I just tried it, and it does not boot.
I get:

FreeBSD/x86 ZFS enabled bootstrap loader. Revision 1.1
ZFS: can't find pool by guid.


> I also don't think there is any merit in aligning to 1MiB. Most ZFS IOs
> will be aligned to sector size (ashift). Unless ZFS pool is created with
> higher ashift then the 63 sector offset is as good as any.

Aligning to the Erase block:

http://blog.nuclex-games.com/2009/12/aligning-an-ssd-on-linux/
Also I will be forcing ashift to 12 using the gnop trick.

If you still feel that is not necessary, I would be interested in 
knowing why?

Thanks,

Cody



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