I defrag my myth xfs filesystem as that runs fairly full (ie a few Gb free on 3.7Tb - blame Denise!) and is used for writing video streams.

Not much entertainment value though :

Jun 6 07:35:03 teak fsr[1227]: xfs_fsr -m /proc/mounts -t 7200 -f /var/tmp/.fsrlast_xfs ...
Jun 6 08:30:19 teak fsr[1227]: Completed all 10 passes
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LittleBlueThing Running twin 30's