[Ocfs2-users] superblock backups, ASM vs OCFS2

[Jeremy Schneider]

[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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://oss.oracle.com/pipermail/ocfs2-users/attachments/20071213/1ad0c422/attachment.html