Infrastructure Raid Mismatch Count SOP

What to do when a raid device has a mismatch count

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Fedora Infrastructure Team


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In some situations a raid device may indicate there is a count mismatch as listed in:


Anything other than 0 is considered not good. Though if the number is low it’s probably nothing to worry about. To correct this situation try the directions below.


More than anything these steps are to A) Verify there is no problem and B) make the error go away. If step 1 and step 2 don’t correct the problems, PROCEED WITH CAUTION. The steps below, however, should be relatively safe.

Issue a repair (replace mdX with the questionable raid device):

echo repair > /sys/block/mdX/md/sync_action

Depending on the size of the array and disk speed this can take a while. Watch the progress with:

cat /proc/mdstat

Issue a check. It’s this check that will reset the mismatch count if there are no problems. Again replace mdX with your actual raid device:

echo check > /sys/block/mdX/md/sync_action

Just as before, you can watch the progress with:

cat /proc/mdstat