Setting Larger AU Sizes in 11GR2

  • From: Lou Avrami <avramil@xxxxxxxxxxxxxx>
  • To: <oracle-l@xxxxxxxxxxxxx>
  • Date: Wed, 23 Mar 2011 18:23:50 -0400 (EDT)

Hi all,

I've been tasked with building an 2-node RAC database on Solaris 10.  
It has been estimated that the database will grow to at least 20 TB, possibly 
as large as 80 TB.

I was reading MetaLink Note 368055.1 - "Deployment of very large databases 
[10TB to PB range] with Automatic Storage Management (ASM)".  This doc, which 
seems more 10g focused, suggests changing the Allocation Unit size to 16MB and 
the strip size to 1MB, via the underscore parameters _asm_ausize and 

In the ASM Configuration Assistant, the Advanced Options button brings 
up several additional options when creating a new disk group - Allocation Unit 
sizes of 1MB, 2MB, 4MB, 8MB, 16MB, 32MB and 64MB.

How can an optimal size be determined? 

We do have an existing database, not RAC or ASM, which is approximately 5 TB.

I was thinking of using a block size of at least 32k for the new RAC database.  
This is a classic Data Warehouse application, with hourly data loads and 
DW-type of aggregate queries.

Should I go with the 16MB recommendation of note 368055.1? 
Under what circumstances should a larger AU size be considered?  A smaller AU 

Lou Avrami 

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