Re: ASM parameters

From: Charles Hooper <>
Date: Fri, 25 Jan 2008 14:10:52 -0800 (PST)
Message-ID: <>

On Jan 25, 2:28 pm, Mladen Gogala <> wrote:
> On Fri, 25 Jan 2008 03:43:42 -0800, Charles Hooper wrote:
> > I don't use ASM, but there may be some hints provided in "Cost-Based
> > Oracle Fundamentals" to explain what you are seeing.  Paraphrased from
> > that book:
> > Oracle uses MBRC from the SYS.AUX_STATS$ for cost calculations, but the
> > runtime engine tries to use DB_FILE_MULTIBLOCK_READ_COUNT when
> > performing physical reads.  On Start up, Oracle determines the operating
> > system's largest physical read size and silently uses that to limit
> > whatever value is set for DB_FILE_MULTIBLOCK_READ_COUNT.
> > You might also want to take a look at the following regarding the
> >
> Charles, ASM is a physical layer, volume manager in user space. I am
> just trying to increase the  read-ahead to speed up backups. ASM cache
> is very much like file system cache, not like the DB cache. I am afraid
> that CBO doesn't have much to do with it.
> This would be analogous to increasing the block size of the underlying
> file system.
> --

Thanks for the clarification. With the inclusion of DB_CACHE_SIZE, DB_FILE_MULTIBLOCK_READ_COUNT, and MBRC, I jumped to the conclusion that you were performance tuning data retrieval, rather than RMAN performance.

A quick Google search found a couple interesting articles that might be helpful:
While the following is specific to Oracle 11g (most will likely apply to 10g R2), it does discuss how ASM requires slighly different parameters for optimal performance. You have probably already found this article, but I thought that I would post it any way:

This document discusses the significance of some of the hidden Oracle parameters that control memory available to RMAN:

Charles Hooper
IT Manager/Oracle DBA
K&M Machine-Fabricating, Inc. Received on Fri Jan 25 2008 - 16:10:52 CST

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