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Re: DataGuard

From: Mladen Gogala <>
Date: Tue, 16 Jan 2007 09:00:56 -0500
Message-id: <>

On 01/16/2007 08:37:23 AM, Polarski, Bernard wrote:
> I am reading this list every day and I must say that the general mood of
> most interveners is that RAC, at least low end RAC, have a bad record in
> term of HA. Many expressed the opinion that a single instance has a
> better HA and this is due to the weakness of complexity of RAC. I will
> add that low end RAC, typically 2 nodes have less skilled people working
> on it. I assume that 'Yahoo' which runs a 32 nodes RAC has a bunch of
> highly skilled RACmen.

Bernie, as someone who has been working with RAC for a long time and who has been working with both the daddy and grandpa of RAC (OPS and VAXCluster) I can tell you that working with RAC is not much different then working with a single instance. You ALWAYS get what you pay for, so cheapo RAC configuration is likely to be Found On the Road Dead ("FORD" for short).

> But we can only express opinion, since there is no statistics, official
> or unofficial on RAC performances versus single instances.

Performance of higher level RAC systems is vastly improved by large amounts of SAN cache and high end machines, built for fast I/O, unlike traditional SMP PC motherboards. Performance of lower lever RAC machines must be improved by functional partitioning. Functional partitioning means that things that related should be done on the same node. One node should be mostly devoted to payroll, finance and such, one node to CRM, one node to rule them all, one node to find them....

> If my boss rush in the room and ask me to swear that RAC is better in
> term of HA, I would be annoyed. On one side RAC is supposed to be more
> HA but on the other side its complexity gives him bad reputation.

RAC does give you better survivability, no question about that. You can restart an instance, without having a database outage. Mainly, the problem with RAC is that people do not understand what are they doing.

> In my current portfolio of DB to manage, I have a newly born RAC,


> In fact, I am implementing RAC but I am not convinced that service will
> be better. Boss read Oracle propaganda, boss pay me, RAC is good in my
> contractor CV, so let's do it. Will it be better.... no idea.

I can recommend reading Kevin Closson's blog, it's an excellent reading. If ever there was a RACman, Kevin deserves the title.

Mladen Gogala

Received on Tue Jan 16 2007 - 08:00:56 CST

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