WARNING with regards to running xfs_fsr

[Ian Hardy <I.D.Hardy@soton.ac.uk>]

I note that my exchange of emails with Steve Lord yesterday
"Re: XFS NFS server Oops" with regards to checking for 
fragmentation and reducing fragmentation using 'xfs_fsr' has 
generated a followup thread "Re: Fragmentation (was: XFS NFS
server Oops)" and some interest in deframenting XFS file systems.

I'd recommend that you DON'T all rush to run 'xfs_fsr', at least
until we've got some more feedback/info from the XFS experts
at SGI. As advised I ran 'xfs_fsr' last night, it had completed
when I got into work in the morning, so I ran 'xfs_db' in order
to check fragmentation levels again:

    # xfs_db -r /dev/md0
    xfs_db: frag -f
    Segmentation fault (core dumped)

Whats more it then shutdown the filesystem (from 'messages'):

Mar 20 09:30:17 blue00 kernel: xfs_force_shutdown(md(9,0),0x8) called from line
1039 of file xfs_trans.c.  Return address = 0xc01e2179 
Mar 20 09:30:17 blue00 kernel: Corruption of in-memory data detected.  Shutting
down filesystem: md(9,0) 
Mar 20 09:30:17 blue00 kernel: Please umount the filesystem, and rectify the
problem(s) 

I rebooted the server and ran 'xfs_check' on the filesystem that showed
a number of errors, which 'xfs_repair' fixed (I'll post some more details
shortly).

While its (very) possible that the above problem was due to underlying
problems with my filesystem, it is also possible that 'xfs_fsr' had
some bad effect on the filesystem. Worth getting some feedback from the
XFS experts before too many people rush to run 'xfs_fsr' !?

By the way I seem to remember a lot of SGI Irix users (including me) had
various problems with 'xfs_fsr' when SGI first introduced it (or enabled
its default running from cron) under Irix a few years ago. I believe
these problems where fixed, however, I still don't routinely run 
'xfs_fsr' on my Irix servers.


Ian

/////////////Technical Coordination, Research Services////////////////////
Ian Hardy                                   
Computing Services                         
Southampton University                      email: idh@soton.ac.uk
Southampton  S017 1BJ, UK.                         i.d.hardy@soton.ac.uk
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