Re: mismatch_cnt > 0 during initial sync?

[NeilBrown <neilb@suse.com>]

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On Tue, Apr 25 2017, Stephane Thiell wrote:

> I just did some tests and this seems normal if one of the raid disk previously has some non-zero data.  Perhaps there should be a note about that in md(4) or elsewhere? (sorry if I missed it)

From the perspective of md, the initial sync is no different from any
other sync.  It will count the number of mismatches that it finds and
fixes.

Feel free to post a patch for md.4 or elsewhere to clarify this.

Thanks,
NeilBrown


>
> Thanks,
>
> Stephan
>
>> On Apr 24, 2017, at 3:01 PM, Stephane Thiell <sthiell@stanford.edu> wrote:
>> 
>> 
>> Hi all,
>> 
>> Is it normal to get any mismatch_cnt > 0 during the initial sync? I just created a few new new raid6 volumes, and one of them is showing an increasing number of mismatch_cnt during its initial resync. Nothing is visible in the console nor after a smart short test (I also started a long test just in case).
>> 
>> 
>> $ mdadm --detail /dev/md7
>> /dev/md7:
>>        Version : 1.2
>>  Creation Time : Mon Apr 24 10:07:18 2017
>>     Raid Level : raid6
>>     Array Size : 62511163904 (59615.29 GiB 64011.43 GB)
>>  Used Dev Size : 7813895488 (7451.91 GiB 8001.43 GB)
>>   Raid Devices : 10
>>  Total Devices : 10
>>    Persistence : Superblock is persistent
>> 
>>  Intent Bitmap : Internal
>> 
>>    Update Time : Mon Apr 24 14:52:12 2017
>>          State : clean, resyncing 
>> Active Devices : 10
>> Working Devices : 10
>> Failed Devices : 0
>>  Spare Devices : 0
>> 
>>         Layout : left-symmetric
>>     Chunk Size : 64K
>> 
>>  Resync Status : 24% complete
>> 
>>           Name : oak-io1-s2:7  (local to host oak-io1-s2)
>>           UUID : 6ece9d71:a97f9497:4612ed73:44dfdc0a
>>         Events : 3308
>> 
>>    Number   Major   Minor   RaidDevice State
>>       0     253       62        0      active sync   /dev/dm-62
>>       1     253       63        1      active sync   /dev/dm-63
>>       2     253       72        2      active sync   /dev/dm-72
>>       3     253       75        3      active sync   /dev/dm-75
>>       4     253       89        4      active sync   /dev/dm-89
>>       5     253       87        5      active sync   /dev/dm-87
>>       6     253      119        6      active sync   /dev/dm-119
>>       7     253       97        7      active sync   /dev/dm-97
>>       8     253      103        8      active sync   /dev/dm-103
>>       9     253      107        9      active sync   /dev/dm-107
>> 
>> $ cat /sys/block/md7/md/sync_completed
>> 3795284824 / 15627790976
>> 
>> $ cat /sys/block/md7/md/mismatch_cnt 
>> 3424
>> 
>> versions:
>>  mdadm-3.4-14.el7_3.1.x86_64
>>  CentOS7 (3.10.0-514.10.2.el7_lustre.x86_64)
>> 
>> Thanks!
>> 
>> Stephan
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