A question from a Twitter following:

Is it not overkill for an organization with fewer than 100 mailboxes and a single site to have a DAG implemented?

Database availability groups are the high availability building block for Exchange Server. The question of whether or not to implement a DAG should always be one that is approached in terms of business requirements instead of user count. A highly available email service may be very important to those 100 users, or even to 50 or 10 users. If the business need outweighs the cost, then why not deploy a solution that meets those needs?

Perhaps the organization already has a robust, highly available virtualization platform deployed, with reliable internet connectivity and a software licensing agreement that makes it trivial to deploy an additional Exchange VM to form a DAG.

Of course, the existence of Office 365 means that deploying a highly available on-premises may not be the most cost-effective approach. There’s no correct answer because each customer and their associated costs and other factors are different, but you’ll often find there’s a sweet spot where it’s most cost-effective to use Office 365 than to try and provide high availability on-premises.

But ultimately, the answer is no. It’s not overkill if the customer requires that level of availability.

About the Author

Paul Cunningham

Paul is a former Microsoft MVP for Office Apps and Services. He works as a consultant, writer, and trainer specializing in Office 365 and Exchange Server. Paul no longer writes for Practical365.com.


  1. Hakeem Abdulsalam

    Thank you Paul

  2. Hakeem Abdulsalam

    Thanks again for this piece.

    Since DNS RR is not really efficient in a production environment and you actually need two public IPs to make it work (provided you have two CAS box).

    My question is, for an organisation that want their Mails to be highly available and don’t have enough to invest on an expensive load balancer. what will be your advice for this kind of people.

    Secondly, are there any free efficient LB out there that you know of?

    And also have you ever had/have a customer still using DNS RR or NLB for CAS HA and if yes what was your reaction?


    1. Avatar photo
      Paul Cunningham

      DNS RR is perfectly fine in a production environment.

      Yes you need two public IPs or a load balancer.

      A company that wants high availability but doesn’t want to invest in a load balancer has their priorities all wrong.

      Yes there are free load balancers that are easy to find by searching Google or Bing.

      Yes I have customers using DNS RR and it works fine. None of my customers use NLB because it is unsuitable for load balancing Exchange.

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