RE: ASM mirroring vs SAM mirroring
Not having done ASM but how does ASM do mirroring across a geographical ("stretched") 
cluster when the two storages are seperated by a significant distance ?
I know that CA mirrors at the storage level but how does ASM read the disks (devices) from the two storage units together ? What network does it use to replicate between 
the two failure groups ? How does it handle latency ?

At 08:36 PM Friday, Peter McLarty wrote:

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. 


________________________________

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 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 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.




Hemant K Chitale
http://hemantoracledba.blogspot.com

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