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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