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_at_xs4all.nl]
>Sent: Fri 27/07/2007 8:12 PM
>To: Peter McLarty
>Cc: oracle-l_at_freelists.org
>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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