superblock backups, ASM vs OCFS2
- From: "Jeremy Schneider" <jeremy.schneider@xxxxxxxxxxxxxx>
- To: Oracle-L <oracle-l@xxxxxxxxxxxxx>
- Date: Thu, 13 Dec 2007 10:50:52 -0600
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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