RAID 1 Mismatches

[Raman Gupta]

On 12/29/2009 09:27 AM, Michael Cronenworth wrote:
> Rick Wagner on 12/28/2009 09:41 PM wrote:
>> 1) Where can the errors be coming from? I would understand if a
>> drive were reporting errors. Could it be during boot, one of the
>> R-1 members is being written too before MD is started?
>
> If you have X running, you can start palimpset and view SMART data. If
> you don't have X running, you can run "devkit-disks --dump" to view
> SMART data. Look for "reallocated sectors", "uncorrectable sectors", or
> "pending sectors", and if they are not showing 0 for current value, then
> you have bad sectors forming.

The OP already said he didn't have any drive errors...

I also have the same problem -- my RAID-1 array regularly has a 
non-zero mismatch_cnt. For a RAID-1 array, this isn't *necessarily* a 
problem, especially with swap or mmap'ed files on the array. See this 
post on the CentOS mailing list for more info:

http://lists.centos.org/pipermail/centos/2009-December/086667.html

Cheers,
Raman