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RE: More than 2 ASM Diskgroups in a RAC Enviornment with 2 Databases

From: Mark W. Farnham <>
Date: Fri, 9 Mar 2007 13:07:46 -0500
Message-ID: <018e01c76275$d8ccbae0$>

Let me take a quick run at this. We have a bit of a language problem regarding the word "general." In science, a general theory must apply to all cases. In the vernacular about "best practices" and otherwise you will find the word "general" used in a way that means "the commonly found special case."  

Here are a few things off the top of my head that are characteristics of the commonly found special case I hope Oracle refers to:  

  1. The disks/disk arrays you have operate at the same speed.
  2. No database or process loads exist that you must protect from each other.
  3. The disks/disk arrays you have are uniform in need for ASM to provide or not provide additional redundancy.

These issues have little or nothing to do with size. There might also be reasons to have more disk groups simply to group them by some maximum size, but I find as things get huge you reach reasons to be a little more sophisticated in the disk group construction so I have not hit any size limits.  

I believe the best practice described in this case is intended to give you a minimized initial construction cost and balance in load across the disk farm.  

I posted something a bit longer a while ago that some folks thought was a useful summary of the cases, and if you want to consider things in depth beyond that I think Morle's stuff about Sane SAN is useful next step. If a simple flat profile is all you need, then SAME in the two described bits is a simple baseline to implement.  

But please don't confuse balance with optimal.  


From: [] On Behalf Of Naqi Mirza
Sent: Friday, March 09, 2007 2:06 AM
To: K Gopalakrishnan; Oracle-l List
Subject: Re: More than 2 ASM Diskgroups in a RAC Enviornment with 2 Databases  


This is from the the ASM Best Practices Document on OTN. See page 12 of 39, under diskgroups and databases:
To reduce the complexity of managing asm and its diskgroups, Oracle Recommends that generally no more than two diskgroups be maintained and managed per RAC cluster or single ASM Instance. .
That said, I didn't mean to imply its not supported or not possible - I, only, inferred this from the above.
That said, I proceeded to test the install, with the details below - and its all good - works fine (so far).



Which document you are talking about? We never say 'no more than 2 disk groups per cluster'.

Btw your initial plan seems perfect.


On 3/7/07, Naqi Mirza <> wrote:
> I see a similar question to this has already been posted, but just
> if anyone's actually had to configure something like this before.
> ----- Original Message ----
> From: Naqi Mirza <>
> To: oracle-l <>
> Sent: Wednesday, 7 March, 2007 2:07:47 PM
> Subject: More than 2 ASM Diskgroups in a RAC Enviornment with 2 Databases
> Hi,
> ---- Start ----
> Config Details:
> 2 Node 10gR2 RAC
> HP-UX (PA-RISC) 64 Bit, 11.23
> Serviceguard 11.17
> ASM used as storage option for database and recovery files.
> ---- End ----
> This 2 node cluster will host 2 RAC databases. Looking at the best
> document for ASM, I see it says that typically you should have no more
> 2 diskgroups per RAC cluster.
> However, the initial plan was to create 4 diskgroups - 2 for each
> Just wondering if anyone has done something similar to this, or if anyone
> has more than 1 rac database using asm as the storage?
> Thanks
> Naqi
> ________________________________
> The all-new Yahoo! Mail goes wherever you go - free your email address
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Best Regards,
K Gopalakrishnan
Co-Author: Oracle Wait Interface, Oracle Press 2004

Author: Oracle Database 10g RAC Handbook, Oracle Press 2006




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Received on Fri Mar 09 2007 - 12:07:46 CST

Original text of this message