Re: superblock backups, ASM vs OCFS2

Jeremy,
asmcmd, in 11.1.0.6 already has a 'backup' command (and a restore). Is it enough? I haven't tried it yet to see what it can recover.

rgds

On Dec 13, 2007 8:03 PM, Jeremy Schneider <jeremy.schneider_at_ardentperf.com> wrote:

> OCFS2 and ASM both support async and directIO (note 279069.1)**.
> Performance-wise, I'm pretty sure that there's not a big difference one way
> or the other for day-to-day operation. There may be some minor differences
> when extending files or creating new ones but I don't think that they're
> anything to fuss over.
>
> Since there's no major difference in performance-related capabilities, for
> me the choice would probably hinge on other factors.
>
> - OCFS2 is open-source. (+1 for power-users!)
> - OCFS2 already does superblock backups. (+1 for recoverability.)
> - ASM is integrated with Database Console/Grid Control. (+1 for
> manageability.)
> - ASM does cluster-aware volume management. (+1 for flexibility.)
>
> I do think that the last one is a strong point in favor of ASM. Volume
> management really can simplify things. And with ASM you get volume
> management and still have a single point of contact for any bugs you
> discover - no finger-pointing. Also, I don't know of any open-source LVM
> that I'd really want to use to do any kind of redundancy - so if you need
> software mirroring on linux then I think that ASM is really the best
> solution for you. And if you want ease-of-management then ASM is better in
> that area too.
>
> Now you could get volume management and stay open-source with OCFS2 by
> using cLVM. However I don't think that cLVM currently supports mirroring or
> parity. IBM's EVMS also has cluster functionality and is GPL - but from the
> release history and mailing lists it seems like noone's maintaining it
> anymore. And I think you can buy ServiceGuard for Linux and get
> cluster-aware volume management there too. There might be more commercial
> solutions that I'm not aware of.
>
> Not to mention GFS, which I'd also really like to spend more time learning
> someday. GFS has its own feature called "pools" which also provide volume
> management though I think that RedHat is moving toward cLVM for cluster
> volume management with GFS. You can run your Oracle RAC database on GFS
> (note 329530.1) but if there are any filesystem-related bugs then Oracle
> will tell you to call RedHat for the fix (note 423207.1).
>
> Anyway, just some random musings... I've always liked being able to dig
> into the source code of whatever's running on my systems so I'm kindof keen
> on OCFS2... but it does appear that the general push is toward ASM these
> days.
>
> DB+RAC+ASM/OCFS+OEL+Oracle VM... is there anything Oracle doesn't do
> these days? Next year I'm anticipating Oracle Open Office... after all
> it's the final frontier...
>
> ========
> Addendum: while I was writing this email there were a few responses on the
> ocfs-users list (I cross-posted).
>
> Definitive answers:
> OCFS: "Backup superblock has been available with ocfs2-tools 1.2.3 (Mar
> 2007)."
> http://oss.oracle.com/projects/ocfs2/dist/documentation/ocfs2_faq.html#BACKUPSB
>
>
> ASM: "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."
>
> So it looks like OCFS backs up your superblock as long as you got it after
> March. And it is often possible to reconstruct an ASM disk header and
> backups will be made in 11.1.0.7 and beyond. And if you ever wondered
> what that KFED tool was for...
> ========
>
>
> On 12/13/07, Finn Jorgensen <finn.oracledba_at_gmail.com> wrote:
> >
> > 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_at_ardentperf.com > 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
> > >
> >
> >
>
>
> --
> Jeremy Schneider
> Chicago, IL
> http://www.ardentperf.com/category/technical
>

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