26 things I shouldn’t forget about Exchange 2010 DAG, nor should you!

I am currently involved in planning and designing a couple of site resilient Microsoft Exchange 2010 clusters so I have been reviewing my notes and here is one I would like to share with you.

In short it is the summary of  an 11 pages long technet document in 26 points I had previously highlighted on papers.

  1. Each Mailbox server in a DAG must be a member server in the same domain.
  2. A domain controller running Exchange 2010 Mailbox server cannot be added to a DAG
  3. DAGs are available in both Exchange 2010 Standard Edition and Exchange 2010 Enterprise Edition.
  4. A DAG can contain a mix of servers running Exchange 2010 Standard Edition and Exchange 2010 Enterprise Edition.
  5. All members of a DAG must run either Windows Server 2008 or Windows Server 2008 R2. They can’t mix
  6. All members of a DAG should be running Enterprise version of Windows
  7. Using a single network in each DAG member is a supported configuration
  8. It is recommended that a each DAG have at least 2 networks
  9. When configured with a single NIC the DAG network does not need to be enable for replication and should be configured as MAPI network
  10. Each DAG member must have the same number of networks
  11. Each DAG member must have no more than one MAPI network
  12. Each DAG membermust have round trip network latency no greater than 250 ms
  13. IPv6 is supported only when IPv4 is also used.
  14. A pure IPv6 environment isn’t supported.
  15. A DAG requires additional IP addresses when the MAPI network is extended across multiple subnets.
  16. At any specific time, the cluster for the DAG will use only one of the assigned IP addresses.
  17. DAGs with an odd number of members do not use a witness server.
  18. There is no requirement that the version of the Windows Server OS of the witness server match the operating system used by the DAG members.
  19. In an active/passive configuration, no users are normally hosted in the standby datacenter.
  20. In an active/active configuration, users are hosted in both locations.
  21. Each datacenter will require its own unique namespace for the various Exchange 2010 services in that site.
  22. MAPI networks should be isolated from Replication networks
  23. Client-facing DNS records should have a Time to Live (TTL) of 5 minutes
  24. automatic activation of the mailbox databases in the second datacenter can be blocked
  25. If aDAG is extended across multiple datacenters, the majority of the nodes should be in the primary datacenter
  26. If each datacenter has the same number of members, the primary datacenter hosts the witness server

ref: Planning for High Availability and Site Resilience

I have been working in IT consultancy and solution integration since 1998 and I consider myself lucky to be, one in a few, making a living out of my passion. I am also member of the famous Experts Exchange (profile here) online community where I try my best to share what I have learned along the road.

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4 comments on “26 things I shouldn’t forget about Exchange 2010 DAG, nor should you!
  1. Mireille says:

    maybe you should create a slide on slideshare.net with the different points

  2. MarkD says:

    In reference to number 23. Client-facing DNS records should have a Time to Live (TTL) of 5 minutes
    The article doesn't specifically mention the DAG name to be set to a TTL of 5 minutes. The dag name isn't client facing. I have tried to set the DAG name dns TTL to 5 minutes but the DAG group will automatically change it back to 20 minutes. Is this correct or am I missing something?

    • Zachary Loeber says:

      Clustering services will automatically update the DNS address with a TTL of 20 minutes. If testing a failover scenario you can manually change the ttl each time after it has been updated though.

  3. Dnash says:

     I have 2 Nodes in Primary Site/ 1 Node in DR- Site. Primary Site has a Mapi Network and Replication Network. In DR Site can I have a Mapi-Network and ISCSI Network and force DAG replication traffic from Primary Site Replication Network to DR-Site Mapi Network?

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