Re: Setting Larger AU Sizes in 11GR2

From: Greg Rahn <greg_at_structureddata.org>
Date: Wed, 23 Mar 2011 17:47:11 -0700
Message-ID: <AANLkTimWdNxAT8CSAeTwnJzTSVvPJXPRBQsN5=te6EmT_at_mail.gmail.com>

I'd suggest reading the ASM intro guide as it does discuss these topics: http://download.oracle.com/docs/cd/E18283_01/server.112/e16102/asmcon.html

With 11g the ASM AU parameters are not hidden, they are disk group attributes http://download.oracle.com/docs/cd/E18283_01/server.112/e16102/asmdiskgrps.htm#CHDHIDEH

For example:
CREATE DISKGROUP data NORMAL REDUNDANCY
FAILGROUP controller1 DISK

'/devices/diska1',
'/devices/diska2',
'/devices/diska3',
'/devices/diska4'

FAILGROUP controller2 DISK

'/devices/diskb1',
'/devices/diskb2',
'/devices/diskb3',
'/devices/diskb4'

ATTRIBUTE

'compatible.asm' = '11.2',
'compatible.rdbms' = '11.2',
'sector_size'='4096';

As many know, I'm a big fan of 8k blocks unless rows dont fit in an 8k block or larger blocks are beneficial for LOB related reasons. The reason is simply that 8k is the most tested block size and there is generally very little gains. If you logic is simply "I have a big DW so I need a big block size", you should probably stick to 8k.

On Wed, Mar 23, 2011 at 3:23 PM, Lou Avrami <avramil_at_concentric.net> wrote:
> I've been tasked with building an 11.2.0.2 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 _asm_stripesize.
>
> In the 11.2.0.2 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 size?

-- 
Regards,
Greg Rahn
http://structureddata.org
--
http://www.freelists.org/webpage/oracle-l

Received on Wed Mar 23 2011 - 19:47:11 CDT