[CentOS] /etc/cron.weekly/99-raid-check

Thomas Harold thomas-lists at nybeta.com
Tue Dec 1 13:36:49 UTC 2009


On 12/1/2009 8:05 AM, Paul Bijnens wrote:
> I have the problem on 2 servers, and both of those servers are also running
> a VMware image (very small, but constantly used) under VMware Server 2.
> Could it be that the .vmem file, or even the virtual disk is constantly
> written to, and the raid is constantly out of sync because of that?
> (All my other VMware servers have hardware raid cards; or are still on
> Centos4.)

... that fills me with dread.  The whole point of RAID-1 is supposed to 
be that data that gets written to one drive also gets written to the 
other drive.  But yes, apparently will see this on systems where the 
file is being constantly written to.

http://bergs.biz/blog/2009/03/01/startled-by-component-device-mismatches-on-raid1-volumes/

http://www.issociate.de/board/goto/1675787/mismatch_cnt_worries.html
(this is a post from 2007 that discusses the issue)

http://forum.nginx.org/read.php?24,16699

Apparently, a non-zero number is common on RAID-1 and RAID-10 due to 
various (harmless?) issues like aborted writes in a swap file.

http://www.centos.org/modules/newbb/viewtopic.php?topic_id=23164&forum=37

Also mentions that it can happen with VMWare VM files.

And lastly, "please explain mismatch_cnt so I can sleep better at night".

http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=405919

So my take on all of that is, if you see it on RAID-5 or RAID-6, you 
should worry.  But if it's on an array with memory mapped files or swap 
files/partitions that is RAID-1 or RAID-10, it's less of a worry.


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