[DRBD-user] repeatable, infrequent, loss of data with DRBD

Matthew Vernon mcv21 at cam.ac.uk
Thu Aug 27 15:21:24 CEST 2015

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


On 22/08/15 10:07, Lars Ellenberg wrote:

> Did you try the same with a variation of:
> create: "echo MAGIC STRING | dd oflag=direct conv=sync bs=4k count=1"
> verify: "dd iflag=direct bs=4k count=1 | xxd -a"

I have now done this, and I still see the same failure rate of ~1:1000. 
I actually used:

echo "TESTDATAMAGIC" | dd oflag=direct conv=sync status=none bs=4k 
count=1 of=/dev/drbd2


ssh ${remhost} "dd status=none iflag=direct bs=4k count=1 if=/dev/drbd2 
| xxd -a | grep -F 'TESTDATAMAGIC' >/dev/null"

> Also, lvm.conf "preferred names" is not good enough.
> You need to actually deny use of the lower level devices.

The lower level device is filtered out ( with filter = [ 
"r|^/dev/guests/mwsig-|" ] ).

I will now try and get more detailed output as you suggest; I wanted to 
check that I still saw errors with dd'ing a particular string rather 
than pvcreate before re-writing my test code to log more details.



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