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

From: Goulet, Dick <richard.goulet_at_capgemini.com>
Date: Mon, 21 Jan 2008 13:29:55 -0500
Message-ID: <746B47FAF6783042B256C0E7CC0795CD026B6041@caonmastxm02.na.capgemini.com>

Dan,  

            I think you're tapping right around the key issue here which is what is the effect on the business of an application being down? I've heard a lot of people calling for maximum availability architectures where there is no single point of failure, but then we get into the "what's this going to cost" part of the discussion & things then get really messy. I've seen a VP complain that we were "halving" the capacity of a disk array just so that we could have mirroring of the drives. His contention was that we had not seen a drive failure in the last 3 years, what made us think that one would happen in the next 3. The problem isn't the technology, but the business implications thereof that are not understood and consequently get into projects doomed to failure in the first place. Now I've a current client with a WEB facing application who has done the math and for them having a 4 hour down time due to equipment failure is "acceptable". That being established a two level standby configuration more than makes their expectations (one standby local, the other remote). So, IMHO, maximum availability is something that we have to define application by application with the most critical application dictating the solution for the database selected. Zero down time is like absolute zero or the speed of light easy to define, impossible to attain.  



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

Together: the Collaborative Business Experience



From: Dan Norris [mailto:dannorris_at_dannorris.com] Sent: Monday, January 21, 2008 12:53 PM
To: Goulet, Dick; mssql_2002_at_yahoo.com; oracle-l_at_freelists.org Subject: Re: RAC Vs Standby Database between Primary and Secondary Data Centers  

Dick,

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 http://www.oracle.com/technology/deploy/availability/htdocs/maa.htm.

Dan

  • Original Message ---- From: "Goulet, Dick" <richard.goulet_at_capgemini.com> To: mssql_2002_at_yahoo.com; oracle-l_at_freelists.org Sent: Monday, January 21, 2008 9:24:26 AM Subject: RE: RAC Vs Standby Database between Primary and Secondary Data Centers

Bob,

    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 / www.capgemini.com Fax: 508.229.2019 / Email: richard.goulet_at_capgemini.com 45 Bartlett St. / Marlborough, MA 01752

Together: the Collaborative Business Experience  

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Received on Mon Jan 21 2008 - 12:29:55 CST

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