[Ocfs2-users] superblock backups, ASM vs OCFS2

[Saar Maoz]

To avoid confusion, the paragraph I wrote is in context of ASM's 
management of superblock, not OCFS2.  OCFS2 was already responded to by 
Sunil in another reply.

Regards,

Saar.

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On Thu, 13 Dec 2007, Saar Maoz wrote:

> Date: Thu, 13 Dec 2007 20:28:44 +0200 (Jerusalem Standard Time)
> From: Saar Maoz <Saar.Maoz at oracle.com>
> To: Jeremy Schneider <jeremy.schneider at ardentperf.com>
> Cc: ocfs2-users at oss.oracle.com
> Subject: Re: [Ocfs2-users] superblock backups, ASM vs OCFS2
> 
> Jermey,
>
> In 11.1.0.7 (and beyond) we will have a backup of the disk header (the first 
> 4k).  Prior to that, we have been able in most circumstances to reconstruct 
> the disk header using KFED.  KFED will still be the tool to restore the disk 
> header going forward, it will just be a simpler, more reliable procedure.
>
> Regards,
>
> Saar.
>
> --
>  __  _    _  __    _ _   _   _ ___ _____________________________
> ((  /\\  /\\ ||)  |\V/| /\\ /\\ >/ Consulting Software Engineer
> _))//-\\//-\\||\  |||||//-\\\\//<_ Oracle Corporation
> HQ: 650.50-mixOS  WK: 510.222.4224 Saar.Maoz at oracle.com  4op441
> \\\\\\\\50-64967\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
> ///Share your knowledge with others and compete with yourself///
>
>
> On Thu, 13 Dec 2007, Jeremy Schneider wrote:
>
>> Date: Thu, 13 Dec 2007 10:58:44 -0600
>> From: Jeremy Schneider <jeremy.schneider at ardentperf.com>
>> To: ocfs2-users at oss.oracle.com
>> Subject: [Ocfs2-users] superblock backups, ASM vs OCFS2
>> 
>> [Also posted to Oracle-L]
>> 
>> Just wondering, does anyone know much about "superblock" backups in ASM vs
>> OCFS2?
>> 
>> I ran into an interesting case a month or so back where someone had
>> accidentally tried to initialize their ASM disks with linux LVM...  and
>> written the LVM headers to the disk.  It was just a few bytes at the very
>> top of the disk - but it was enough to totally hose ASM.  Which started me
>> thinking, "if this was a filesystem then I'd have a backup superblock that 
>> I
>> could recover".  Who knows - maybe ASM has a backup of its header block -
>> but it's all proprietary and if there's a tool that will recover an ASM
>> header then it's probably buried at Oracle support somewhere.
>> 
>> Looks like OCFS2 includes superblock backups since this patchset:
>> http://lkml.org/lkml/2007/1/22/148
>> 
>> Not sure if ckfs will recover them but since it's open source it'd be
>> trivial to put together a utility that would recover a superblock.
>> 
>> This seems to me to be a great reason to choose OCFS2 over ASM.  Recovering
>> a backup superblock is MUCH faster than recreating the entire volume and
>> restoring data from backup!!!  I don't even know if you could use dd to try
>> to backup your ASM disk headers - since it's proprietary I don't know 
>> what's
>> in those blocks.
>> 
>> Anyone have any thoughts on this?  Is there anything I'm missing here?
>> 
>> Jeremy
>> 
>> 
>> -- 
>> Jeremy Schneider
>> Chicago, IL
>> http://www.ardentperf.com/category/technical
>> 
>> 
>
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