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I use Gentoo Linux both at home and at work. Every so often I hit some snag and I'd like to detail the fix here both for my benefit and to possibly help anyone else having a similar issue.

Friday, March 14, 2008

XFS fragmentation

Check your fragmentation levels:
# xfs_db -c frag -r /dev/vg/lv1
actual 37387, ideal 35541, fragmentation factor 4.94%
# xfs_db -c frag -r /dev/vg/lv2
actual 688725, ideal 667471, fragmentation factor 3.09%
# xfs_db -c frag -r /dev/md3
actual 631947, ideal 624800, fragmentation factor 1.13%

On Gentoo, xfs_db is in sys-fs/xfsprogs which, if you have an XFS filesystem, you should already have installed.

If you want to run the defragger, the command is xfs_fsr and on Gentoo you need to install an additional package, sys-fs/xfsdump, to get it. You can read the manpage on xfs_fsr for more info, but the gist is if you don't otherwise supply command line params it will start going through all of your xfs mountpoints and stop after either 10 passes or 7200 seconds. It keeps track of where it was so you can just run it again and it will pick up where it left off if it didn't make it through all 10 passes.

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