DataCenter Failover

Hello all

Running Exchange 2013 CU8. Currently we have a 5 node DAG that is stretched across two datacenters. 3 nodes in the primary DC and 2 nodes in the secondary DC. The FSW is located in the primary DC.  Because we have three copies of every DB all the databases are configured for circular logging enabled = True. The DAG is configured in an Active\Active mode, meaning we have mounted databases in both datacenters, and we have an unbound namespace model. After activating all the databases in the secondary datacenter and running in this configuration for 24 hours, will the database log files continue to be purged, because i have Circularlogging enabled? If this is true then when it comes time to add the nodes in the primary DC back to the DAG, how will the database copies in the primary DC get up to date with the active copies in the secondary DC? If the database copies in the primary DC are offline, because those nodes are no longer in the DAG, and because Circular logging in enabled, i do not understand how the database copies in the active DC can become up to date?

Tha

July 14th, 2015 2:54pm

Take a look at this post detailing Continuous Replication Circular Logging (CRCL). Under this mode, logs won't be deleted unless they've been replicated and replayed (according to lag settings - see the article for full conditions).

When you say add the nodes in the primary DC back, I'm assuming you're referring to bringing them online after a failure. Those nodes should get their copies up to date based on the logs (that haven't been deleted since the conditions above weren't achieved, due to the primary nodes being offline).

The key to the whole processes is stated in the article: "As a result, unlike Jet circular logging, when you enable CRCL, the current log file is not overwritten and closed log files are generated for the log shipping and replay process."

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July 14th, 2015 3:39pm

you are correct, i do mean bringing the nodes back into the DAG. From your explanation it sounds like the log files generated since the time the nodes in the primary DC were removed from the DAG will not be purged, even if circularlogging is enabled for the databases?

Thank you again. I will read the article you posted

July 14th, 2015 4:11pm

Hi skipster,

Thank you for your question.

I agree with Albert and you are right. If the circular logging file will not be deleted if the node in the primary DC was removed from DAG, because the log will not be replicated.

If there are any questions regarding this issue, please be free to let me know.

Best Regard,

Jim

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July 14th, 2015 10:30pm

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