Normally top reports CPU line, sy at 0.4% when idle. If I format an external Firewire disk
as btrfs and mount it, it remains at 0.4%. If I reformat as XFS and mount it, again top
reports sy at 0.4%. However, if I reformat as ext4 and mount it, sy runs at 3.5%. These
two processes are now at the top of top's results:
Each uses on average 1.9% CPU. The light on the external drive flashes 4x per second.
There are no processes using the disk at all while this is going on. If I umount it, the
pulsing stops. If I remount it, the pulsing resumes as does the slightly higher CPU
This doesn't happen with the same hardware mounted XFS or btrfs or HFS+.
These reveal nothing related to the disk:
lsof | grep sdb
lsof | mapper
If I sift through it unfiltered with the volume mounted and not, I don't really see
anything obvious standing out.