Re: ASM parameters

From: Charles Hooper <>
Date: Fri, 25 Jan 2008 03:43:42 -0800 (PST)
Message-ID: <>

On Jan 25, 3:46 am, Mladen Gogala <> wrote:
> on RH Linux 4.0, update 4, 2 node RAC. I am experimenting with
> Default cache size is 25M, MBRC is 110. Default block size is 4k.
> I have set cache size to 128M, MBRC to 256 (1M reads). I tried going above
> 1M, but the parameter was ignored. RMAN seems to work much faster,
> benchmark is in progress. Does anybody have any recommendations or
> experiences to share?
> --
> Mladen Gogala

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 DB_FILE_MULTIBLOCK_READ_COUNT parameter:

Charles Hooper
IT Manager/Oracle DBA
K&M Machine-Fabricating, Inc. Received on Fri Jan 25 2008 - 05:43:42 CST

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