Ext3 users - Apr 2009 - Superblock missing, FS corruption after power outage

Hi all,

I'm wondering if its possible that an ext3 filesystem with journaling
enabled
and so on (defaults really) could lose its primary superblock and lose, in
this case, a whole directory which contained a virtual server.

It is possible in this case that a fair chunk of data could have been lost as
the RAID card has a 256mb cache with no battery backup for cached data, but it
seems somewhat extreme that the superblock went missing (according to mount
the filesystem didn't exist, according to fsck.ext3 it had to use a backup
superblock), and that a whole directory disappeared and didn't end up in
lost+found.

During the fsck there were lots of claims of inodes claiming the same data
blocks as some other inodes and as such the fsck chose to clone those blocks.
 In some instances - well, at least one, a directory that contained PostgreSQL
databses became a symbolic link to some python file after the fsck.

So I'd like to know if all of this is possible just from a power failure, or
if there is something else going on that was possibly causing file system
corruption that wasn't noticed until the reboot.

Thanks.

--
Regards,
Robert Davidson.

On Apr 21, 2009  19:17 +1000, Robert Davidson wrote:
> It is possible in this case that a fair chunk of data could have been lost
as
> the RAID card has a 256mb cache with no battery backup for cached data,
At this point, all bets are off - ext3+jbd expects when the disk reports
that data is safe on disk that it really is safe.
> seems somewhat extreme that the superblock went missing (according to mount
> the filesystem didn't exist, according to fsck.ext3 it had to use a
backup
> superblock), and that a whole directory disappeared and didn't end up
in
> lost+found.
Well, if you lost 256MB at the start of the filesystem then that could easily
contain the whole directory, which might only be a few blocks in size.

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.