Hi,

I'm with client that has 4 Exchange/AD sites: Virgiinia, California, UK and Germany.

All sites are well connected. Each Database has 3 copies total (CA and VA sharing copies, UK and Germany sharing copies). What would be the best solution in this scenario to have one DAG or 2 DAGS (one for europe and one for America)? Please factor in the scenario where the link between Europe and North America goes down even though there are no databases being share between the two conti

I recommend that you hire an experienced consultant to work through this and other issues with you.

Hi,

I recommend pay attention to below link about Database availability groups and Exchange 2010 Tested Solutions with two sites(especially, steps 8 in Determine High Availability Strategy section):
https://technet.microsoft.com/en-us/library/dd979799(v=exchg.150).aspx
https://technet.microsoft.com/en-us/library/gg558613(v=exchg.141).aspx

You can do it testing in your lad before modify your product environment.

Thanks

I can't determined what would happen in this scenario:

One DAG for 4 sites and each site has 2 Exchange servers: UK, Germany, California and Virginia. Primary FSW is in CA and alternative in VA. 

If the WAN link between Europe (UK, Germany) and USA (CA, VA) was to go down unexpectedly, USA has majority votes and would win over the quorum and hence the Europe database will failover to USA. Let me know if I am incorrect on this. But what if Europe does not have any copies in USA, what would happen then in this one DAG scenario? Will any of the databases dismount or failover, or remain the same?

Your failover assumption is correct.  If there are no copies in the USA, the Europe databases would dismount.  They wouldn't be able to fail over if there were no copies anywhere else.

It is possible to have some database in DAG without any database copies.

But Exchange considers such DAG unhealthy.

I do not understand your question.

Hi Ed,

But there are copies in Europe between UK and Germany.  Does that mean Europe databases will dismount if the wan link between europe and US is down? US has 5 votes and Europe has 4 votes. (perhaps this is a lost quorum in europe).

It's not the number of database copies, it's the number of voting members of the DAG and the tie-breaking file share witness that determines quorum.  Voting members are servers in the DAG.

You can create databases in the DAG with a single copy, the mounted copy, and no replicated copies.  You may get warnings or errors in the event log, and you are welcome ignore them.  It's a supported configur