Re: iostat - multiblock read count

From: Fabrizio <fabrizio.magni_at_mycontinent.com>
Date: Wed, 25 May 2005 10:52:38 +0200
Message-ID: <42943cf0_1@x-privat.org>

Noons wrote:
> Fabrizio wrote:
>
>

>>Is this a Redhat limit?

>
>
> AFAIK, yes. That's why it is in the RedHat Bugzilla.
> It's not really a limit: just a default design decision of
> the 2.4 kernel people, I guess. And only for 2.4 kernel level.
> Ie, supposedly fixed in RHAS4 which is kernel 2.6 (or so I'm told...).
>

I had a look at the associated bug on metalink. It seems the limit of 32K involves only i/o on raw and OCFS of a specific redhat version.

I cannot see any limit in 2.4 kernel related to i/o (at least I couldn't spot any references in the source code or in the kernel mailing list).

As a test I took an old vanilla kernel (2.4.12) and performed the previous dd (always on ext3 and reiserfs). The limit is not there and the asynch i/o is doing its duty.

The interesting thing about the bug you pointed out is that it shows only on OCFS and raw devices: those use synch OS i/o instead of aio. I would conclude that it is really a redhat issue only.

May I ask you the sources of your statement about a 2.4 "design limit"? (I'd like to invastigate this further: so far it smmes a myth).

>
>
> Yup, very much so. Which happens to involve all disk IO.
> See the best practices pdf link posted before for details.
>

Thank you. The document (and the related ones) is really useful.

-- 
Fabrizio Magni

fabrizio.magni_at_mycontinent.com

replace mycontinent with europe

Received on Wed May 25 2005 - 03:52:38 CDT