[CentOS] puzzling md error ?

Clint Dilks clintd at scms.waikato.ac.nz
Sun Feb 28 23:43:04 UTC 2010

On 01/03/10 11:37, John R Pierce wrote:
> Clint Dilks wrote:
>> SWAP inside LVM is fine in my experience.  Personally I consider this a
>> benign error and generally ignore it unless the mismatch count is very high
> And how do I know all these mirror data mismatches are Swap?  does not
> each mismatch mean the mirrors disagree, which means one of them is
> wrong.  Which one?  since they aren't timestamped or checksummed (like
> vxvm, zfs do), I am playing 'data maybe'.    As someone who adminstrates
> database servers, i have a real problem with that.
> btw, this is centos 5.4+latest x86_64, its primarily running postgres,
> and our inhouse java middleware apps.  and was going to be a oracle grid
> operations server.
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Even if this isn't SWAP the issue is to do with aborted writes.  As I 
understand it. Situations occur where a write is requested, written to 
1st drive but then aborted. There are two ways this can be handled.  
Drive 2 doesn't have the data on it yet so doesn't matter.  But Drive1 
you can either delete the unwanted block and then mark it as free.  Or 
you can just skip the delete.  The second option is what Software Raid 
does.  So the differences being detected all relate to blocks that 
marked as free for re-use.

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