= Infrastructure Raid Mismatch Count SOP

What to do when a raid device has a mismatch count

== Contents

* <<_contact_information>>
* <<_description>>
* <<_correction>>

== Contact Information

Owner::
  Fedora Infrastructure Team
Contact::
  #fedora-admin, sysadmin-main
Location::
  All
Servers::
  Physical hosts
Purpose::
  Provides database connection to many of our apps.

== Description

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

....
/sys/block/mdX/md/mismatch_cnt
....

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.

== Correction

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
....