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RE: Active/Passive "high availability"

From: Allen, Brandon <>
Date: Fri, 13 Apr 2007 10:45:37 -0700
Message-ID: <04DDF147ED3A0D42B48A48A18D574C45071FDA58@NT15.oneneck.corp>

I've noticed there seems to be some disagreement about whether or not RAC is really a "High Availability" solution. There is no doubt that Oracle advertises it as such:  

E.g. from .pdf:  

"Oracle RAC provides very high availability for applications by removing the single point
of failure with a single server. If a node in the cluster fails, the Oracle Database
continues running on the remaining nodes. Individual nodes can be shutdown for
maintenance while application users continue to work."  

And here: signing_%20ha_systems_with_rac[1].pdf  

On page 13 there is a graphic of RAC with a mirrored disk subsystem, and again the claim of "No Single Point of Failure"  

So, it seems to come down to how you define a "single point". If you look at the "database" as a single point, then yes there is a SPOF, but if you look at it more granularly and consider that the database resides on hardware with mirrored disks and multiple controllers, fibre channels, fans, power supplies, etc. - then there isn't really a SPOF at the database level either because it would really require multiple failures to bring down the database.  

A disaster such as flood, fire, earthquake, vandalism, etc. could easily bring down the entire disk array at once, but that falls under the category of Disaster Recovery, not HA and I think we all agree that RAC is generally not a DR solution although I believe some are running RAC with the nodes geographically dispersed in an attempt to incorporate DR as well.  


[] On Behalf Of Jared Still

A single RAC system with a single database (also a SPOF) is also not HA.

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Received on Fri Apr 13 2007 - 12:45:37 CDT

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