Re: San-Based replication VS DataGuard replication

From: Madison Pruet <>
Date: Fri, 03 Oct 2008 14:24:45 GMT
Message-ID: <>

DA Morgan wrote:
> macdba321 wrote:

>> Group,
>>  I have a database at Site1 stored on a SAN, and a disaster-recovery
>> site2 with identical hardware. They are connected by high-speed fiber.
>> (Both SANs are enterprise-class with full journaling capabilities in
>> case the connection were ever severed.)

> 4. Data Guard, interestingly enough, is more efficient. What is being
> replicated is the transactions themselves not operating system
> blocks so are shipping less data.

This does not make sense. SAN based replication is done only when a physical write occurs. Since DG is pushing the logs to the secondary to achieve replication, it is replicating for any change in the page. Unless Oracle is flushing every page to disk as it is updated, then the impact to performance for a SAN based solution should be much more efficient than pushing the logs to the secondary.

Also consider the case with hot pages, such as index pages. DG will be forced to send each update to the page to the secondaries while SAN based replication will only replicate the page as it is flushed to disk.

The only logical way that DG could be more efficient would be if the Oracle database flushes every dirty page to disk as it is updated. I can see the logs being flushed immediately, but the data and index pages???? Is that the case? Received on Fri Oct 03 2008 - 09:24:45 CDT

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