Exchange 2013 - Two DAG member split between two DCs


We have an Exchange 2013 server with all roles: CAS, HUB, Mailbox in our existing DC.  Our compliance requires email resilience and therefore, we would like to configure a secondary node with all roles in a secondary DC.

Could someone please assist me if the server in the secondary DC will manually mount without any issues in the following cases:
- VPN dropping between the two DCs
- Exchange server in the primary site crashing/stopped

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Simon Butler (Sembee)ConsultantCommented:
You really do NOT want the second server to mount automatically when the VPN drops. I would go as far as to say I wouldn't want the server in the second data centre to activate automatically for any reason at all.
That would cause a split brain scenario, which you want to avoid. Split brain is basically both servers being active, and therefore when they reconnect, both have changes to the database which cannot be resolved.

Every design I do for a dual data centre approach does not have automatic failover involved. It is always manual. The reason for that is simply the loss of the VPN/Internet connection between the two servers is the most likely cause.
Instead most clients will have a set procedure to go through for certain scenarios. Loss of the VPN in most cases is not a failover event, because it can be quite common.


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