CERC Performance Question

[Celso K. Webber]

Hello,

I believe you should also do a 'sync' before and after the 'dd' comand, and
thus sum up both values measured by the 'time' command.

For instance:
# sync
# time dd of=/dev/zero if=big_file bs=1024 count=5120000
...
# time sync
...

And then sum up both values to get a real measurement of performance without
being influenced by Linux caching.

Regards,

Celso.

On Wed, 26 Jul 2006 15:54:59 +0200, Tino Schwarze wrote
> On Wed, Jul 26, 2006 at 03:42:18PM +0200, Florent Gilain wrote:
> > Hi all,
> > 
> > I have many PE1850 and 2800 with Perc4 raid card with 2 RAID 1 Hard disk,
> > here is what i get :
> > 
> > [root at apache1 usr]# date; dd if=/dev/zero of=big_file bs=1024 count=5120000;
> > date
> > mer jui 26 15:33:31 CEST 2006
> > 5120000+0 enregistrements lus.
> > 5120000+0 enregistrements écrits.
> > mer jui 26 15:35:59 CEST 2006
> > [root at apache1 usr]# date; dd of=/dev/zero if=big_file bs=1024 count=5120000;
> > date
> > mer jui 26 15:36:41 CEST 2006
> > 5120000+0 enregistrements lus.
> > 5120000+0 enregistrements écrits.
> > mer jui 26 15:38:31 CEST 2006
> > 
> > This seems very bad performances no ?
> 
> You can use "time dd of=/dev/zero if=big_file bs=1024 count=5120000" 
> to get a more precise measurement...
> 
> Bye,
> 
> Tino.
> 
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--
Celso K. Webber <celso at webbertek.com.br>
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