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RE: ASM mirroring vs SAM mirroring

From: Tony van Esch <>
Date: Fri, 27 Jul 2007 20:46:04 +0200
Message-Id: <>

Hi Peter,

In the EVA SAN there is always some kind of 'mirroring/redundancy' involved (VRAIDx), but not across storage boxes. Another interesseting point to consider is what to do with the voting disk(s). You need an uneven amount of votingdisks to run a cluster. If you use 1 vote, this is a Single Point Of Failure. Next up is a three vote config, but then you need some kind of independent third storage unit separate from the two EVA's.

Tony van Esch

-----Oorspronkelijk bericht-----
Van: [] Namens Peter McLarty
Verzonden: vrijdag 27 juli 2007 14:37
Aan: Tony van Esch
Onderwerp: RE: ASM mirroring vs SAM mirroring

Hi Tony  

Your information is much appreciated.  

From all the HP Papers it was never clear about such stuff, I guess you had to have the presentation with them.  

Now I can at least make plans around those requirements  

It seems from things I had heard about that some other technologies supposedly allow you to do both mirror at teh HW level and ASM.  

Will have to consider this information in regards to the DR plans and test this failure out. This is still being implemented and have time to desing the document on failures if they should occur.  



From: Tony van Esch [] Sent: Fri 27/07/2007 8:12 PM
To: Peter McLarty
Subject: Re: ASM mirroring vs SAM mirroring


we have a similar config running (DUAL HP EVA, mirroring and RAC) and asked the suppliers (HP & Oracle) what would be a certified solution. In the end ASM was the only viable solution.

1> mirroring on SAN level with EVA is called 'Continuous Access'. You 1> only
get presented the primary LUN's, but not the copy. The copy is NOT presented to the racnodes. So if the storagebox/site with the primary LUN's fails, you lose your disks and your database is gone and you have downtime. Not really flexible. the mirror woulf have to be presented to the racnodes to get things up & running.

2> Mirroring with ASM (host-based mirroring). Is this case the primary 2> and
the copy are both presented to the racnodes and placed inside the correct failuregroups (FG1=site1/storagebox1 and FG2=site2/storagebox2). If one storagebox/site fails, only one failuregoup is lost, but the database will still be available.

So if you distribute racnodes of one cluster over two datacenters mirroring for the databases should be done with ASM. I'm even not sure Continous Access is supported for shared storage.

Tony van Esch

> Hi all
> Not being a storage guru, I need some help
> I have been through the papers on racsig and done some googling "asm
> mirroring" and looking for product specific papers and cant find
> anything definitive as to why one is a winner and not the other
> Here is my scenario
> 2 HP EVA8000 SANS
> RAC cluster
> ASM for storage on said SANS
> The two SANS are in different datacenteres about 1km apart.
> Some cluster nodes reside in each datacentre.
> Oracle Redhat 4 nodes
> Question is ASM mirroring better than SAN mirroring? Why is it better
> or not Sould we use the HP SAN mirroring product
> Cheers
> --
> Peter McLarty
> Database Administrator
> Student System Upgrade Project
> Central Queensland University
> --


Received on Fri Jul 27 2007 - 13:46:04 CDT

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