Re: AIO on ASM

sagyvolkov_at_gmail.com wrote:
> Hi,
>
> I read that ASM instance comes with AIO enabled by defualt (probably
> filesystemio_options=asynch and disk_asynch_io=true), does anyone know
> if the instances (RAC in my case) that are using the ASM diskgroups
> needs also to be setup with AIO enabled or since all DB relevant files
> reside on the ASM there is no need to?
>
> Also, anyone knows if i need to get any special AIO libs for redhat EL
> 4 and do i still need to enable the oracle binary with 10.1.0.4.0 or is
> it enabled automaticaly?
>

Hi Sagy.

To use AIO on linux oracle *needs* to be relinked against libaio. So you must install the packages: libaio and libaio-devel.

On 10gR1 aynch I/O is not enabled by default (even with ASM). To proof this:

oracle_at_breousdbls02:~> ps -fe|grep dbw

oracle    5474     1  0  2005 ?        00:00:00 asm_dbw0_+ASM
oracle   17596     1  0  2005 ?        00:15:19 ora_dbw0_UBANKP
oracle    3213  3175  0 15:05 pts/1    00:00:00 grep dbw

oracle_at_breousdbls02:~> sqlplus "/as sysdba"

SQL*Plus: Release 10.1.0.4.0 - Production on Wed Jan 4 15:04:30 2006

Copyright (c) 1982, 2005, Oracle. All rights reserved.

Connected to:
Oracle Database 10g Enterprise Edition Release 10.1.0.4.0 - Production With the Partitioning, OLAP and Data Mining options

SQL> show parameter filesystem

NAME                                 TYPE        VALUE
------------------------------------ ----------- 
------------------------------
filesystemio_options                 string      none

oracle_at_breousdbls02:~> grep kio /proc/slabinfo
kioctx                 0      0    256   15    1 : tunables  120   60 
  8 : slabdata      0      0      0
kiocb                  0      0    128   30    1 : tunables  120   60 
  8 : slabdata      0      0      0

The zeros indicates that no aio is being used.

So to enable AIO you need:

1. relinking against libaio,
2. set filesystemio_options to asynch or setall (I explain this below).

On 10gR2 things are different.
Relinking against libaio is not necessary (and possible) anymore and the RDBMS is AIO capable by default even if filesystemio_options is set to none (it must be changed to "asynch" if you want to use that kind of I/O on a filesystem).

Tests on 10gR2 with ASM show differences between filesystemio_options=none and filesystemio_options=asynch. Slabinfo indicates that AIO is being used in both cases but the syscalls are different. I'm still trying to determine if there are permonce differences.

In any case, even with ASM, filesystemio_options is still important.

If needed I can post the testing steps and results.

Regards.

-- 
Fabrizio Magni

fabrizio.magni_at_mycontinent.com

replace mycontinent with europe