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I have my Dag for Exchange Server 2016 deployed in such a way that 1 x Mailbox is on Primary site and 1 x Mailbox is on Secondary Site. My Witness Server is also on the Secondary Site for now (which is temporary as we wanted to test failover by temporary turning primary site off). But recently due to some power outage my Secondary site went down and along with it my witness server. I was unable to connect to my Primary mailbox server as well which i think was because my witness was down. As i tried to open the exchange admin center, it never went through the login page.
In the end when the connection to witness server was again established, i had to restart my DAG (both mailboxes) for the re-connectivity to exchange admin center.
We don't have any third site for placing the witness server. It will be either on Primary or secondary site.
Is there any solution which can help in such a situation i.e incase the witness is down? We want the other site's mailbox to work even if one site is down (which does work only when witness is online).
I have read about DAC mode, but i don't think it will work either in my case as it is mostly used to avoid split brain.
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Hi @Usama A. Rub ,
Do you still have any questions? If your issue is resolved, you could mark the useful reply as an answer, which will help others in the community.
Well, DAC mode is the really the only option. it would allow you to bring up the secondary site and set a file share witness at the same time so the quorum and databases could be mounted in the second site with manual intervention.
If you do not have a 3rd data center for the FSW which would allow high availability as well as site resilience , then this your only option.
Will DAC mode work even if Witness Server is down? Also, will it work with only one remaining DAG member (as the other one will be down aswell)?
I read the whole document on DAC but couldn't quite understand how it will help in my case. Can you please elaborate?
Yes, when you activate the DAG members in alternate data center, you also set the new file share witness so the DAG can reach quorum:
https://learn.microsoft.com/en-us/exchange/high-availability/manage-ha/datacenter-switchovers?view=exchserver-2019
One thing to note. There is NO requirement that the DAG is in DAC Mode to make this work, however DAC Mode allows you to use the build in Exchange commands to handle the data center switchover and helps prevent split-brain clusters.
Okay, so basically this implies that i will have to manually do the data center switchover.
Please clear one more confusion. It says in the screen shot above that if there is an "even number" of DAG members. But won't i be left with only a single member as i have 1 member in each site. and when one of the site is down i will be left with an odd member?
(Sorry if you find my questions basic, as i have no other means of help and i am the only one managing the server. I would really be obliged if you could also suggest a training for exchange server )
Yes you have only one member left standing, but the DAG itself is still even-numbered in the configuration.
Now there is a concept of dynamic quorum that will come into play - however with only 2 members total in your DAG, it probably wont apply:
https://social.technet.microsoft.com/wiki/contents/articles/32325.exchange-2013-how-does-dynamic-quorum-work-for-a-two-node-dag.aspx