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Exchange 2013 - Powering off old mailbox servers caused 100% cpu on CAS servers :-(

Posted on 2016-10-26
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Last Modified: 2016-11-01
We recently build new mailbox servers on newer hardware and added them to the DAG. Databases were moved off the old servers, connectors copied etc, connectors disabled on the old servers.

Today we planned to power these servers off for 7 days. Was a bit of a disaster - both our CAS servers went to 100%. Slowly recovering now because we powered back on.

I must admit I thought they were dead. Or would they still have been processing client requests? Whats the best way to decomm these servers? Or should I have removed from DAG?
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Question by:paulfoel
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by:paulfoel
ID: 41860064
Hmm. Looks like windows clustering had something to do with it. We left 4 mailbox servers on and powered off 5 of them.

Looks like some of the windows clusters stayed in a failed state.
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by:Simon Butler (Sembee)
Simon Butler (Sembee) earned 2000 total points
ID: 41860324
The power off and see what breaks method doesn't work for Exchange.
Exchange expects the servers to be there and gets upset when they are not.
Therefore the "results" of tests like that are void because you will see problems.

If you have removed all of the mailboxes and taken the servers out of the DAG, then remove the databases and remove Exchange using add/remove programs. If something is still using them then the installer will tell you and not let you continue.
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by:paulfoel
ID: 41861740
No we hadnt removed them from the DAG. I think that was the problem - windows cluster got in a right state.

So you would recommend removing from the DAG maybe one at a time?
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by:paulfoel
ID: 41861741
I still dont understand why windows clustering got in such a state though? Surely if we'd legitiimately lost half our servers it should still be able to run?
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Simon Butler (Sembee) earned 2000 total points
ID: 41861845
If the plan is to remove the servers for a power off scenario then you should have removed them from the DAG.
How many servers in total do you have? Do you have an FSW? It could be that it lost quorum.
The cluster should have stayed active and may well have done - your post though is referring to CAS role. A little more control over the servers is required before powering them off.
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by:paulfoel
ID: 41861945
2 CAS (one of which is the DAG witness).

4 mailbox servers that we're keeping (and have got all the databases on). 5 mailbox servers we turned off.

What then happened was the CPU went to 100% on both of the CAS servers, effectively locking users out. We powered the 5 servers back on but the failover cluster seemed to be in a bit of a state so we had to manually correct that.

Going forward our plan is going to be - one server at a time, remove from dag.
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