[DRBD-user] Slow Access

Stefan Seifert nine at detonation.org
Tue Oct 27 14:36:11 CET 2009


On Tuesday 27 October 2009 15:09:02 gilberto.nunes wrote:

> Drbd works fine but I attempt
> deploy virtual machine with KVM and I feel access to /dev/drb0 is
> slowing...

So you've got two VMs running on the same host and sharing a drbd disk?
That will never be fast even if you do all the performance tuning that's 
documented in the user's guide, the performance seminar, Flo's blog and this 
mailing list.

Virtualization already slows down I/O access dramatically, because for every 
little request there are a few context switches involved. Same goes for 
networking. With drbd you double your I/O requests and add networking on top 
of it. That's all the slowness you could possibly find on your system 
combined.

Using protocol A might improve the situation but with the obvious 
disadvantages. But I assume this setup is only for testing anyway? So don't 
worry too much about performance now and get on to optimizing when it's 
deployed on real hardware. Should make a huge difference.

Regards,
Stefan
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