Mailing List Archive: DRBD: Users

Slow Access

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gilberto.nunes at selbetti

Oct 27, 2009, 7:09 AM

Post #1 of 3 (674 views)
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Slow Access

Hi buddies

I have make a server here, with two nodes, with Ubuntu
9.04.

I config the drbd8-utils, version 2:8.3.0-1ubuntu1, with this conf
on both nodes:

obal { usage-count no; }
common { syncer { rate 30M; }
}
resource r0 {
protocol C;
startup {
wfc-timeout 15;
degr-wfc-timeout
60;
become-primary-on both;
}
net {
cram-hmac-alg sha1;
shared-secret
"drbd123";
allow-two-primaries;
after-sb-0pri discard-zero-changes;

after-sb-1pri discard-secondary;
after-sb-2pri disconnect;
}
on kvm-0 {

device /dev/drbd0;
disk /dev/sda7;
address 10.0.0.10:7788;
meta-disk
internal;
}
on kvm-1 {
device /dev/drbd0;
disk /dev/sda7;
address
10.0.0.100:7788;
meta-disk internal;
}
}

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

Nothing to desperate, but a instalation of Windows 2003 take
some many times! About 2 hours..

I don't know what going happen here!!!

Thanks for any advice

Regards

--
Gilberto Nunes Ferreira
TI
Selbetti
Gestão de Documentos
Telefone: +55 (47) 3441-6004
Celular: +55 (47)
8861-6672

_"BENDITA A NAO CUJO DEUS O SENHOR!"_
<

nine at detonation

Oct 27, 2009, 6:36 AM

Post #2 of 3 (638 views)
Permalink

Re: Slow Access [In reply to]

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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gilberto.nunes at selbetti

Oct 27, 2009, 9:58 AM

Post #3 of 3 (633 views)
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Re: Slow Access [In reply to]

Yes

I just do some test...
But in a real enviroment this performance is preocuped...
Is there some way "allow-two-primaries" work on Protocol A.

Thanks

On Tue, 27 Oct 2009 14:36:11 +0100, Stefan Seifert <nine [at] detonation>
wrote:
> 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

--
Gilberto Nunes Ferreira
TI
Selbetti Gestão de Documentos
Telefone: +55 (47) 3441-6004
Celular: +55 (47) 8861-6672

_"BENDITA A NAO CUJO DEUS O SENHOR!"_
<
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