Oracle FAQ Your Portal to the Oracle Knowledge Grid
HOME | ASK QUESTION | ADD INFO | SEARCH | E-MAIL US
 

Home -> Community -> Usenet -> c.d.o.server -> Re: ORACLE on Linux - IO bottleneck

Re: ORACLE on Linux - IO bottleneck

From: Fabrizio Magni <fabrizio.magni_at_mycontinent.com>
Date: Thu, 09 Feb 2006 22:57:58 +0100
Message-ID: <43ebbae5$0$12598$4fafbaef@reader3.news.tin.it>


Eder San Millan wrote:
>
> I can suppose you are saying that in 2.4 kernels, RAWDEVICES only
> allows 512 byte IOs ??
>

low level? Yep.

>> The first case show direct I/O (syncronous).
>> The second one a buffered I/O.

>
> Direct IO (rawdevices) implies syncronous IO ( at Oracle level ) ?
>

No. I used a dd and the worload was syncronous. Oracle can exploit the kaio capabilities of linux (search for libaio). The difference is in the sycalls used.

>
> So, could we say that RawDevices in 2.4 kernels are not recomended or
> this is supposing too much. We will upgrade to 2.6 kernel but this
> suppose us many problems that must solve with a lot of time and this
> other problem is being done in a productive system and....well...you
> know ...
>

****Test on filesystem before going with 2.6.**** Check if there are performance differences. I used rawdevices on top of LVM on a RAC 9i for a couple of years with good performance (and it was an oooold SLES7).

>> What do you mean saying that your device had 1k block size?!?
>> Isn't you using it "raw"?

>
> Look (maybe I'm saying a blinge):
> ----------------------------------------------------------------
> # blockdev --getbsz /dev/sdc
> 1024

Personally I don't know the --getbsz. I cannot find it in the man pages on the web.
Tomorrow, from office, I'm goign to check the sources of blockdev. I see there is even setbsz. Have yuo tried changing it?

> ----------------------------------------------------------------
> SDC is the device that Storage system present me, this "disk" is part
> of a VG that we divide in many LVs where we link the rawdevices
> This value (bsz=1024) isn't important?
>

Yes, it makes a lot of different (sorry, I didn't ask you if you were using LVM).
On LVM1, lvcreate can specify the readahead value and the "contiguity" (plus tons of other parameters).

I believe now it is time for benchmarking. :)

Maybe tomorrow I can give you more information.

-- 
Fabrizio Magni

fabrizio.magni_at_mycontinent.com

replace mycontinent with europe
Received on Thu Feb 09 2006 - 15:57:58 CST

Original text of this message

HOME | ASK QUESTION | ADD INFO | SEARCH | E-MAIL US