Re: CPU 0.1% IOWAIT 99% for decisonnal queries

Hi!

I have a Dell PowerEdge 2600 with a Perc 4/DI and 4 scsi disks 35GB.
I have made a array raid 0+1 with 4 disks, because is mission critical
application. But, for your, you can configure a raid0, thats is faster
than raid5 for 4 disks.

Ask to your system enginner what is distribution of Linux is used,
kernel version and if he does a kernel tuning for your hardware and
application.

Best regards.

Atenciosamente,

Gustavo Franklin Nóbrega
Infraestrutura e Banco de Dados
Planae Tecnologia da Informação
(+55) 14 3106-3514
http://www.planae.com.br

Patrick Vedrines wrote:

> Great !
>
> I'm not an expert but as far as I know, my 15 databases are spread
> over 4 SCSI RAID disks 73 GB 10K RPM mounted under ext3 mode.
> I remember that they where provided by DELL under RAID5 and I asked my
> system engineer for switching them to standard SCSI because I don't
> care about security but only about speed and capacity ( maybe this
> switch was not set properly at this time...).
>
> Thank you for these interesting links: I 've sent them to my system
> engineer with my two hands !
>
> Amicalement
>
> Patrick
>
> ----- Original Message -----
> *From:* Gustavo Franklin Nóbrega - Planae
> <mailto:gfnobrega(at)planae(dot)com(dot)br>
> *To:* Patrick Vedrines <mailto:patrick(dot)vedrines(at)adpcl(dot)com>
> *Cc:* performance pgsql <mailto:pgsql-performance(at)postgresql(dot)org>
> *Sent:* Thursday, March 24, 2005 12:52 PM
> *Subject:* Re: [PERFORM] CPU 0.1% IOWAIT 99% for decisonnal queries
>
> Good day Patrick!
>
> I can help you to design you disk layout for better perform
> and security. Please, tell me how many disks (and some specs, like
> capacity and RPM).
>
> If you want to know more, there is a very interesting article
> abou benckmark filesystem (
> http://linuxgazette.net/102/piszcz.html ). In this article,
> ReiserFS 3.6, JFS and XFS are in the same level at top depending
> your application, and ext3 is more slow than others. I believe
> that version 4 of the ReiserFS is better that version 3.6, but I
> could not still test it.
>
> Raid0 (striping, more at
> http://www.pcguide.com/ref/hdd/perf/raid/levels/singleLevel0-c.html)
> or Raid 0+1 (stripping + mirror, more at
> http://www.pcguide.com/ref/hdd/perf/raid/levels/multLevel01-c.html)
> is very insteresting to postgresql. Raid0 provides only
> performance, and Raid 0+1 provides performance and security. Take
> a look at this articles and think about to use Raid
> (http://www.pcguide.com/ref/hdd/perf/raid/).
>
> I'm glad to help. Best regards!
>
>Atenciosamente,
>
>Gustavo Franklin Nóbrega
>Infraestrutura e Banco de Dados
>Planae Tecnologia da Informação
>(+55) 14 3106-3514
>http://www.planae.com.br
>
>
>
>
>
> Patrick Vedrines wrote:
>
>> Hello Gustavo,
>>
>> Your question seems to say that you suspect a disk issue, and a
>> few hours later, Simon told me "Sounds like your
>> disks/layout/something is pretty sick".
>> To be clear in my own mind about it, I've just copyed (time cp)
>> the "aggregate" table files (4 Gb) from one disk to an another
>> one: it takes 22 mn !(3 Mb/s).
>> That seems to demonstrate that Postgres is not the cause of this
>> issue.
>> I've just untrusted to my system engineer the analysis of my disks...
>>
>> In case I would have to change my disks, do you have any
>> performance figures related to the types you mentionned (reiserfs
>> vs ext3) ?
>> I don't use RAID since the security is not a concern.
>>
>> Thank a lot for your help !
>>
>> Patrick
>>
>>
>> Hi Patrick,
>>
>> How is configured your disk array? Do you have a Perc 4?
>>
>> Tip: Use reiserfs instead ext3, raid 0+1 and deadline I/O
>> scheduler in kernel linux 2.6
>>
>>
>>