Re: Filesystem vs. Raw IO

On 05/27/2004 01:24:09 PM, Rick Stephenson wrote:
> I just ran some tests and I was shocked at the results. I assume I am
> missing something very obvious.

You are right.

>
>
> Exporting data 2 million row table:
>
>
>
> EMC disk on UFS filesystem: 50 sec
>
> EMC disk raw space: 3 min 8 sec
>
> NetApp disk UFS filesystem: 48 sec
>
> NetApp disk raw space: 3 min 7 sec
>
>
>
> What should I be looking at? Why such a big difference?

Well, during export you mostly read, using full table scan. With UFS, you're doing buffering and prefetch and that speeds things up. With raw devices, you're not doing that. Raw devices are a bit faster when it comes to an active OLTP system. For a read-only database, buffered file systems are actually faster. Your case proves the importance of BCHR and validity of the method "C".

-- 
Mladen Gogala
Oracle DBA



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