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RTURNER asked

Running DBCC CHECKDB in a Passive Node

I am about to put SP4 on SQL Server 2012. https://blogs.msdn.microsoft.com/john_daskalakis/2014/09/05/how-to-install-a-service-pack-at-a-sql-server-2012-failover-instance-best-practices/ Instructs to run DBCC CHECKDB earlier in the process than it instructs to fail the node over to a passive state. Since DBCC CHECKDB is on of the most IO intensive things one can do I would thing the node should be failed over to a passive state before running DBCC CHECKDB. Am I correct in my thought? Must DBCC CHECKDB be run while the node is in a productive state?
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Usman Butt answered
If you consider that at a given time - Only one node is accessible to the users which is why it is called the active node - The system databases and user databases are on the shared storage - Only the active node can read/write from/to the databases You can easily conclude that running the DBCC will have the same effect no matter on which node you run it. Whenever you failover to the passive node, that passive node will become the active node, and all the traffic would be routed to that node. So if you would run DBCC on that node, you could see the performance degradation in any case. Having said that, you can mitigate the performance degradation by restoring the databases to another server and running DBCC there. The added benefit is that you would be able to test your backups as well.
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