mdadm – mismatch_cnt is not 0 on /dev/md0

/etc/cron.weekly/99-raid-check:
WARNING: mismatch_cnt is not 0 on /dev/md0
if uncounted the title's warning in weekly check. We have to do the following to repair and check the array.

echo repair >/sys/block/md0/md/sync_action
echo check >/sys/block/md0/md/sync_action

Ref: http://www.centos.org/modules/newbb/viewtopic.php?topic_id=23164&forum=37
Apparently, a non-zero number is common on RAID-1 and RAID-10 due to 
various (harmless?) issues like aborted writes in a swap file.

So my take on all of that is, if you see it on RAID-5 or RAID-6, you 
should worry. But if it's on an array with memory mapped files or swap 
files/partitions that is RAID-1 or RAID-10, it's less of a worry.

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