Re: superblock backups, ASM vs OCFS2
- From: "Finn Jorgensen" <finn.oracledba@xxxxxxxxx>
- To: jeremy.schneider@xxxxxxxxxxxxxx
- Date: Thu, 13 Dec 2007 12:24:16 -0500
Jeremy,
I don't know the answer to your question but this reasoning :
>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!!!
is like saying you should use MySQL instead of Oracle because if you lose
one file you can just restore that one file and carry on. No downtime, no
recovery. Once human error enters the picture all bets are off. What if your
"someone" had decided to dd a bunch of data into the device your OCFS2
filesystem is built on? Your superblock backup would have been obsolete.
What if the performance requirements for your database aren't satisfied by
OCFS2?
Your question is valid and interesting I just don't see it as a reason to
choose one option over the other.
Finn
On 12/13/07, Jeremy Schneider <jeremy.schneider@xxxxxxxxxxxxxx> wrote:
>
> 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 something I'm missing here?
>
> Jeremy
>
>
> --
> Jeremy Schneider
> Chicago, IL
> http://www.ardentperf.com/category/technical
>
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