Comment # 2 on bug 920205 from Peter van Hoof

> The script does not report mismatches.
> Detecting mismatches isn't really the point of running a 'check'.
> The main point is to read all block and make sure that none of them have gone
> bad (i.e. cannot be read).
> If any blocks are bad, they will automatically be fix (re-writing) if possible.
>   If that isn't possible, the drive will be removed from the array.

I don't think this is correct. My information is that a 'check' doesn't repair
anything. You need to run 'repair' to get the mismatches fixed.

> Mismatches *are* reported by "mdadm --monitor".
> When "mdadm --monitor" notices that a check has finished it looks to see if
> there were mismatches.	If there were it sends email about it.	This should
> happen when the check finished because it came to the end of the array, or
> when the check finished because it was stopped after 6 hours.
> 
> "mdadm --monitor" is run by the "mdmonitor.service" systemd service, and should
> be started whenever any mdarray is started.
> 
> Do you have mdmonitor.service running?

Yes.

# systemctl status mdmonitor
mdmonitor.service - MD array monitor
   Loaded: loaded (/usr/lib/systemd/system/mdmonitor.service; static)
   Active: active (running) since Tue 2015-02-24 01:20:32 CET; 1 months 6 days
ago
 Main PID: 1083 (mdadm)
   CGroup: /system.slice/mdmonitor.service
           ������1083 /sbin/mdadm --monitor -d 60 -m root@localhost --scan -c
/etc/mdadm.conf

> Do you get mail sent to the MDADM_MAIL address in /etc/sysconfig/mdadm?

My /etc/sysconfig/mdadm has default settings, so MDADM_MAIL="root@localhost". I
am not receiving any mail there from mdadm. I just manually tested the mail
account and it worked fine.

At the moment I have

# cat /sys/block/md2/md/mismatch_cnt
16

from the April 1 check so I should have had an email from mdadm... I did a
manual repair of this RAID5 array last month, but obviously the problems are
back. I would love to know which disk is responsible for this so that I can
examine it more closely...