[DRBD-user] blocking I/O with drbd

Andreas Kurz andreas at hastexo.com
Mon Dec 19 16:49:38 CET 2011

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


On 12/19/2011 04:06 PM, Volker wrote:
> hi,
>>> No, the network link is performing fine syncing at 25MB/s without any
>>> problems.
>> are you saying that your machines are still syncing in the background?
> No, theres no (re)sync going on at the moment. I was referring to what
> is currently configured as syncer-rate. If the two systems resync after
> a disconnect, the full 25MB/s are being used without causing any delay.
> the load on the primary even rises, if the drbd-replication is disabled
> while the dd is run.
>> I'd request another brief overview then:
>> - which machine ist primary/secondary and synctarget/-source
> the setup is described here:
> http://public.blafoo.org/drbd/system-specs.txt
> please notice the 'perftest' logical-volume. doing heavy i/o on that
> one, does not cause any harm to the load of the primary OR secondary.
> i've created two top-files while doing the dd. the very first top-output
> shows, what the load usually looks like:
> http://public.blafoo.org/drbd/top-primary.txt
> http://public.blafoo.org/drbd/top-secondary.txt

ok ... still drbd 8.3.8 ... what does "iostat -dx" say during your test?
cat /proc/meminfo is unsuspicious?


Need help with DRBD?

> this shows quite clearly what happens.
> to make it complete, here's the current output of
> "drbdsetup /dev/drbd0 show"
> http://public.blafoo.org/drbd/current-primary.conf
> http://public.blafoo.org/drbd/current-secondary.conf
>> - what type of network link is in use (you're talking of a switch; no
>> good: use a back-to-back connection for optimal performance)
> see above schematic. sadly a dedicated connection is not possible
> because all the nics are in use (eth0 primary connection, eth1 being
> backup and drbd). but see below, the network does not seem to be the
> problem.
>> - what network throughput can you achieve with a simple TCP test
> about 35-40MB/s
> $ scp test-data.dd root at fallback:
> test-data.dd       100%  392MB  39.2MB/s   00:10
>> - what latencies are you seeing i.e. ping times when idle, ping times
>> during dd
> idle and while dd'ing:
> 64 bytes from fallback.content.domain.de.de ( icmp_seq=3
> ttl=64 time=0.093 ms
> - volker
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> drbd-user mailing list
> drbd-user at lists.linbit.com
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