Re: fs corruption

Dave Chinner
2011-04-12T11:02:14Z

On Tue, Apr 12, 2011 at 03:51:20AM -0700, Leo Davis wrote:
> You have a corrupted free space btree.
>
> Err... apologies for my ignorance, but what is a free space btree?

A tree that indexes the free space in the filesystem. Every time you
write a file or remove a file you are allocating or freeing space,
and these tree keep track of that free space.

If you want to know - at a high level - how XFS is structured (good
for understanding what a free space tree is), read this paper:

http://oss.sgi.com/projects/xfs/papers/xfs_usenix/index.html

It's from 1996, but still correct on all the major structural
details.

> I had serial trace from raid controller which i just checked and
> it logged some 'Loose cabling', but this was months back..... not
> sure whether that can be the cause of this.. strange if that is
> the case since it's been a long time

it's possible that it took a couple of months to trip over a random
metadata corruption. I've seen that before in directory trees and
inode clusters where corruption is not detected until next time they
are read from disk....