On 01/27/2013 02:26 PM, Wolfgang Denk wrote:

I have seen "mismatch_cnt is not 0" warnings in the past, but that has
always been with RAID 1 arrays, and with relatively small numbers on
/sys/block/md*/md/mismatch_cnt; my understanding was that this was not
actually critical.

However, after updating to Fedora 18, I get this message from all
updated
systems that have RAID 6 arrays, and with _huge_ numbers of
mismatch_cnt, like that:

fter updating to Fedora 18, I get this message from all updated
systems that have RAID 6 arrays, and with _huge_ numbers of
mismatch_cnt, like that:

# mdadm -q --detail /dev/md0
/dev/md0:
        Version : 1.2
  Creation Time : Mon Jan 14 14:20:34 2013

Something is missing from this story.  Was the original system created
this month, and immediately upgraded?  Or was there a "mdadm --create"
in this story you haven't told us about?

     Raid Level : raid6
     Array Size : 1459617792 (1392.00 GiB 1494.65 GB)
  Used Dev Size : 243269632 (232.00 GiB 249.11 GB)
   Raid Devices : 8
  Total Devices : 8
    Persistence : Superblock is persistent

    Update Time : Sun Jan 27 02:27:28 2013
          State : clean 
 Active Devices : 8
Working Devices : 8
 Failed Devices : 0
  Spare Devices : 0

         Layout : left-symmetric
     Chunk Size : 16K

           Name : XXX:0  (local to host XXX)
           UUID : da015f96:138b37bf:d5ef71dc:8970ab15
         Events : 8

    Number   Major   Minor   RaidDevice State
       0       8       49        0      active sync   /dev/sdd1
       1       8       65        1      active sync   /dev/sde1
       2       8       81        2      active sync   /dev/sdf1
       3       8       97        3      active sync   /dev/sdg1
       4       8      113        4      active sync   /dev/sdh1
       5       8      129        5      active sync   /dev/sdi1
       6       8      145        6      active sync   /dev/sdj1
       7       8      161        7      active sync   /dev/sdk1
# cat /sys/block/md0/md/mismatch_cnt
362732152


This is with mdadm v3.2.6 (mdadm-3.2.6-7.fc18.x86_64); except for the
huge values of mismatch_cnt, I see no other indications for errors on
the disk drives, RAID arrays or the file systems on top of these.

Is this some known (and hopefully harmless), issue, or must I worry
about our data?

I would be worried, but there's not enough information here to say.

Please share the output of "mdadm -E /dev/sd[defghijk]1".

Please also explain/share what you've done to conclude the filesystem is
error-free.

Phil