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Re: fs corruption

To: Leo Davis <leo1783@xxxxxxxxx>
Subject: Re: fs corruption
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Tue, 12 Apr 2011 21:05:32 +1000
Cc: xfs@xxxxxxxxxxx
In-reply-to: <38287.10078.qm@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>
References: <31377534.post@xxxxxxxxxxxxxxx> <20110412094917.GY31057@dastard> <38287.10078.qm@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.20 (2009-06-14)
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....

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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