[DRBD-user] Unusual Performance. Faster one way.

Richard Walmsley rich.sbs at gmail.com
Tue May 12 05:48:48 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.

Hi Philipp,

Sorry for my late reply.

I made those adjustments you had mentioned, however I was still
getting the same results.
Isolating the VMs out of it, I did a few transfer tests between each
machine using rcp. I no longer have the results but I recall I was
getting roughly the same speeds on both. They were what I expected
from the network.

However I've been testing on another cluster at the moment of which is
made up of identical hardware and I'm getting expected results. I
appreciate the replies though. If I can make the time, I'll see if I
can find the cause of whatever it was.


On Mon, Apr 27, 2015 at 6:30 PM, Philipp Marek <philipp.marek at linbit.com> wrote:
>> I'm doing some testing with Ganeti, a cluster-based VM manager, which
>> uses DRBD as the default syncing system between nodes. My test cluster
>> has two nodes, Alpha & Beta. Ganeti provides a way to migrate from one
>> to another, handling DRBD automatically to sync to the node that isn't
>> running the VM.
>> I'm running into an issue that I'm having difficultly understanding.
>> When benchmarking from within the VM, I'm getting drastically
>> different results depending on the node that the VM is running from.
>> The DRBD benchmarks are below;
> ...
>> For comparison, I've done benchmarks with DRBD turned off. These are below;
>> Alpha;
>> Sequential Write: 206.250 MB/s
> ...
>> Beta;
>> Sequential Write: 207.551 MB/
> As the direct write speeds look similar, I'd guess it's network related.
> Try turning the various optimizations off (TCP checksum offloading etc.)
> - if one of the machines generates bad CRCs every so many packets, it will
> mostly limit the data stream in the Primary => Secondary direction
> as that one runs much more packets.

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