Exchange 2016 power down

Brian Corbett 1 Reputation point


We have a 5-node Exchange 2016 DAG. There are 3 nodes in site A (two mailbox servers and a witness) and 2 nodes in site B (two mailbox servers). DAC mode is enabled.

We have to shut down all power to site A for about 24 hours for electrical maintenance. The three nodes in site A and the network between sites A and B will all be shut down for the duration of the maintenance.

I have built a test system as close to production as possible to test whether the nodes in site B will remain up and running when the 3 nodes in site A are down. The test system shows that the nodes will remain operational despite being a minority (2/5) of the cluster.

Can anyone let me know of any problems that they think may occur with the Exchange environment while site A is down? I will be increasing the size of the log drives in site B in anticipation of log file build up, but is there anything else I should do?

Many thanks!

Exchange Server Management
Exchange Server Management
Exchange Server: A family of Microsoft client/server messaging and collaboration software.Management: The act or process of organizing, handling, directing or controlling something.
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  1. Andy David - MVP 134.1K Reputation points MVP

    The quorum is probably staying up because of dynamic quorum.
    Applies to 2016 and above as well:

    Note the FSW is not used in an odd numbered Cluster.

    If you want and can run the DAG in Site B, have at it, but not sure of the value of only two servers in one DC versus three in the other, if one of those in Site B goes down during the maint outage, you are now down to one server and lose all the advantages of the DAG.

    Since you have this planned, why not take advantage of that and build and a third server in SITE B, add DB copies to it and then set the FSW to a server in Site B.
    Now you have three copies in that site and a FSW local to the site ( Since you now will have 6 DAG members the FSW is relevant)
    That way, if you somehow had an issue with a server in Site B during the outage, you will still have 2 copies and redundancy.

    Then, move the quorum and active copies to Site B.

    Once the maint is complete is Site A, bring the network back up first and then each MBX server in Site A, then move the quorum back to Site A if desired
    You can also set the FSW back to Site A as well.

    With DAC mode, this should prevent split brain problems. You will to also probably stop any backups if you are doing them during the outage.
    Once all the cluster is back up and happy, expect a alot of time to replay all the logs generated and that has to be copied over from Site B to Site A.
    Dont move the quorum or copies back till everything shows clear and healthy

    2 people found this answer helpful.

  2. Kael Yao-MSFT 34,341 Reputation points Microsoft Vendor

    Hi,@Brian Corbett
    Since the maintenance is scheduled,you may also plan for a datacenter switchover.
    Here is a Microsoft document on this topic for your reference: Datacenter switchovers

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