Re: RAC Vs Standby Database between Primary and Secondary Data Centers

From: Dan Norris <>
Date: Mon, 21 Jan 2008 09:53:00 -0800 (PST)
Message-ID: <>


Here's where I think we need to make clear what defines "high availability" versus what becomes "disaster recovery". Many sites want/need both. In my dictionary, I define high availability as a system that can tolerate a failure of a single component without affecting the application availability. There's also "fault tolerance", but that starts to get into a whole other world, so let's put that out of scope for now. Disaster recovery in my book is defined as a system that can handle failure of a data center or geographic location without affecting application availability. I acknowledge that many if not most disaster recovery solutions do have some outage associated with their failover, but that outage is generally shorter than the time required to restore/recover the primary site at an alternate location.

Having said that, I don't disagree with your comments, but felt the need to point out that high availability does not necessarily equal disaster recovery. Also, I submit that RAC is not primarily designed as a disaster recovery solution. As another poster mentioned, RAC does have some support for "stretch clusters", but they are not widely used and the MAA still recommends standby database in combination with RAC (at least the last time I read it).

To the OP, I think the MAA has some good ideas if you're looking for architecture decision points. It is online at


  • Original Message ---- From: "Goulet, Dick" <> To:; Sent: Monday, January 21, 2008 9:24:26 AM Subject: RE: RAC Vs Standby Database between Primary and Secondary Data Centers


    RAC is not a High Availability solution in and of itself. A RAC system must have all servers in the same physical location which leaves you vunerable to earth quakes, fires, etc..... Standby database is there to protect you against these types of disasters by placing an identical copy of your database in a separate physical location that presumably will not get hit by the "9/11 factor" at the same time. The first thing you should do is determine what your trying to protect against and then plan accordingly. RAC will protect you against a single server failure in your local data center. Standby can protect you against a single server failure as well, but adds protection for a 9/11 incident at the same time..

Dick Goulet / Capgemini
North America P&C / East Business Unit
Senior Oracle DBA / Hosting
Office: 508.573.1978 / Mobile: 508.742.5795 / Fax: 508.229.2019 / Email: 45 Bartlett St. / Marlborough, MA 01752

Together: the Collaborative Business Experience

-- Received on Mon Jan 21 2008 - 11:53:00 CST

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