Exchange 2016 Multiple DAG across two sites

Question

_{Tuesday, September 4, 2018 11:34 PM}

I need to validate this design. I have 2 AD sites and I will be implementing 2 DAGs for each site in the Active/Passive model. DAG 1 will contains 3 members two members in site A and one passive member in site B and site B will contain two members and one passive member in site A and site A will be the only internet facing site.

All replies (5)

_{Wednesday, September 5, 2018 4:29 PM ✅Answered}

So it's clear you don't need two DAGs, specially if you're working with routable networks in the same Active Directory forest. What you need is an active-active DAG with specific databases set to active and others passive across both sites.

This achitecture is thoroughly explained in the link I posted earlier.

_{Wednesday, September 5, 2018 5:33 PM ✅Answered}

You can and should create one DAG and configure the databases' activation preferences such that they're normally mounted in the site you want them to be mounted, and ensure that they are normally mounted there.

Deploy two servers in each site.

Create a third site with independent network connectivity to each of the other two sites and locate the file share witness there.

This design will allow you to deploy two fewer servers and have better overall high availability.

Finally, deploy Exchange 2016 so you don't have to go through an upgrade as soon.

Ed Crowley MVP "There are seldom good technological solutions to behavioral problems."
Celebrating 20 years of providing Exchange peer support!

_{Wednesday, September 5, 2018 12:59 AM}

Some things to consider if you're planning to create a site resilient DAG.

• You will need at least one routed network (MAPI) between the servers across both sites. Best practice is to have two networks (MAPI and Replication).
• Your DAG cluster quorum will be set to node majority if comprised by an odd number of nodes. If not, you will need a third site to host a file share witness, or an Azure cloud witness.
• You can have lagged database copies in one of your DAG nodes.
• Most antivirus clients, if not configured with the proper exclusions will wreak havoc in your environment when trying to set up DAGs.
• A specific node can't be part of two DAGs.

It's advised you read the link below before setting up your DAG.

https://docs.microsoft.com/en-us/exchange/high-availability/plan-ha

_{Wednesday, September 5, 2018 5:05 AM}

Why do you think you need two DAGs?  I can't imagine what would necessitate that.

Ed Crowley MVP "There are seldom good technological solutions to behavioral problems."
Celebrating 20 years of providing Exchange peer support!

_{Wednesday, September 5, 2018 12:39 PM}

The customer has only 2 sites and each site considered as the main site, so they decided to create 2 DAGs and those sites will be used as a site resilience for each other.