[DRBD-user] drbd not syncing when iscsi-target is running ?

Arnold Hendriks a.hendriks at b-lex.nl
Tue Nov 11 11:37:16 CET 2008

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

I'm running into an odd problem, about which I'm unsure whether it's a 
bug or whether I'm totally misunderstanding how I should set up DRBD or 
whether the tests I'm doing are actually supposed to work.

The setup involves Centos 5, drbd 8.2.6 and iscsitarget 0.4.16 (the open 
source iscsi enterprise target)

I'm setting up a testenvironment with drbd in primary/primary mode on 
two machines, 'm1' and 'm2'

I'm crudely testing whether replication works at all using 'dd':
at m1: dd if=/dev/urandom of=/dev/drbd4 bs=512 count=1 conv=fsync 
oflag=sync seek=0
at m2: less -f /dev/drbd4

Seeing the bytes change, I assume things are working. Now I start 
iscsitarget (ietd daemon) which has been configured to export 
/dev/drbd4, and without doing anything else on the machines, it seems 
the syncs between m1 and m2 have stopped. Doing a new 'dd' on m1 doesn't 
update the data I see on /dev/drbd4 on m2 anymore. After I stop 
iscsi-target, I can see the changes I made on m2. Starting iscsi-target 
makes the problem reappear.

If I tell iscsi-target to run but not to export /dev/drbd4, I can no 
longer reproduce the problem.

All the time /dev/drbd4 is listed as Primary/Primary UpToDate/UpToDate 
on both servers in /proc/drbd.

I do wonder whether iscsi-target is the source of the problem, or if the 
problem is elsewhere and iscsi-target exporting /dev/drbd4 just triggers 
the problem. Does the list have any suggestions on how to look into this 
problem? Or is my testsetup just plain wrong and shouldn't I expect this 
to work at all?


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