linux-kernel - Re: Linux mdadm superblock question.

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Date:	Sat, 13 Feb 2010 15:07:51 -0500 (EST)
From:	Justin Piszcz <jpiszcz@...idpixels.com>
To:	"H. Peter Anvin" <hpa@...or.com>
cc:	Michael Evans <mjevans1983@...il.com>, linux-raid@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: Linux mdadm superblock question.



On Sat, 13 Feb 2010, H. Peter Anvin wrote:

> On 02/11/2010 05:52 PM, Michael Evans wrote:
>> On Thu, Feb 11, 2010 at 3:00 PM, Justin Piszcz <jpiszcz@...idpixels.com> wrote:
>>> Hi,
>>>
>>> I may be converting a host to ext4 and was curious, is 0.90 still the only
>>> superblock version for mdadm/raid-1 that you can boot from without having to
>>> create an initrd/etc?
>>>
>>> Are there any benefits to using a superblock > 0.90 for a raid-1 boot volume
>>> < 2TB?
>>>
>>> Justin.
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>>
>> You need the superblock at the end of the partition:  If you read the
>> manual that is clearly either version 0.90 OR 1.0 (NOT 1.1 and also
>> NOT 1.2; those use the same superblock layout but different
>> locations).
>
> 0.9 has the *serious* problem that it is hard to distinguish a whole-volume
>
> However, apparently mdadm recently switched to a 1.1 default.  I
> strongly urge Neil to change that to either 1.0 and 1.2, as I have
> started to get complaints from users that they have made RAID volumes
> with newer mdadm which apparently default to 1.1, and then want to boot
> from them (without playing MBR games like Grub does.)  I have to tell
> them that they have to regenerate their disks -- the superblock occupies
> the boot sector and there is nothing I can do about it.  It's the same
> pathology XFS has.
>
> 	-hpa
>

My original question was does the newer superblock do anything special or 
offer new features *BESIDES* the quicker resync?

Justin.
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