RE: ASM mirroring vs SAM mirroring

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.

Regards,
Tony van Esch

-----Oorspronkelijk bericht-----
Van: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx]
Namens Peter McLarty
Verzonden: vrijdag 27 juli 2007 14:37
Aan: Tony van Esch
CC: oracle-l@xxxxxxxxxxxxx
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.
 
Cheers
 
Peter

________________________________

From: Tony van Esch [mailto:tvesch@xxxxxxxxx]
Sent: Fri 27/07/2007 8:12 PM
To: Peter McLarty
Cc: oracle-l@xxxxxxxxxxxxx
Subject: Re: ASM mirroring vs SAM mirroring



Hi,

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.

regards,
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 10.2.0.3 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
> --
> http://www.freelists.org/webpage/oracle-l
>
>
>




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