[DRBD-user] md5 sums mismatch

Felix Frank ff at mpexnet.de
Mon Jul 18 10:38:11 CEST 2011

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.


you should keep stuff on-list :-)

On 07/18/2011 10:29 AM, Łukasz Oleś wrote:
> W dniu 11 lipca 2011 10:45 użytkownik Felix Frank <ff at mpexnet.de> napisał:
>> On 07/11/2011 10:32 AM, Łukasz Oleś wrote:
>>> Online verify found 88 4k block out of sync!
>> 350k out of 3TB?
>> I'd venture to say this is what can result from unfortunate bit-flips
>> somewhere along the way.
>> Yes, these are bad to have. Yet, as far as I know, few systems can even
>> protect you from data corruption happening on the way from RAM to HDD,
>> so I disbelieve you're facing a huge problem.
> During last week we have made more tests. Firstly, we repeated the
> test and again there where mismatches. What is more interesting
> corrupted files were on source volume.

Like I wrote - data can be corrupted between your CPU/Mem and HDD. It's
really hard to guard against this.
I've read that ZFS does have defences, but using it atop DRBD will prove
difficult ;-)

> Then we repeated test again but files were copied localy(not via
> iscsi) and drbd was disconnected. Files were ok.
> Any ideas?

Not really. Your iSCSI target cannot likely take the blame, since all it
does is feeding data to DRBD. If your Secondary received sound data,
that means that the iSCSI target fed sound data to DRBD.

DRBD cannot be blamed either, because it does little more than hand down
data to your HDD controller.

I have to admit that it's strange, however. My "misfortune theory"
doesn't really hold if only one machine is affected. How did you make
sure you were writing sound data during your final test?


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