superblock backups, ASM vs OCFS2

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

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Jeremy Schneider
Chicago, IL
http://www.ardentperf.com/category/technical

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http://www.freelists.org/webpage/oracle-l Received on Thu Dec 13 2007 - 10:50:52 CST