I am currently down in New Orleans attending TechEd 2010 and was able to attend a session by Ross Smith IV.  During the presentation Ross brought to our attention a new feature in Exchange 2010 SP1 regarding Outlook behavior is a cross-site (two datacenters) database failover.

As it stands now in the event that a failover would occur in a DAG the outlook client will connect directly to its preferred CAS server which is set at the RPCClientAccessServer property.  So for example, say you have two AD sites.  Each site contains a CAS Array, CAS1 in Datacenter 1 and CAS2 in Datacenter 2.  The preferred CAS Array in this scenario is CAS1 (RPCClientAccessServer).  So, what this means is that the outlook client is going to default to CAS1 and then to its local database in Datacenter 1.   Now, in the event of a Database failure and the Database fails over to a mailbox server in Datacenter 2 the outlook client will have a direct connect to CAS1 and CAS1 will have a direct connect to the mailbox server in Datacenter 2.  In RTM you can only get a redirect to CAS2 by changing the RPCClientAccessServer property on the database.

In Exchange 2010 SP1 you can choose to enable or disable cross-site direct connect.  You can also define an activation preference for a database which determines whether to perform a direct connect or a redirect. 

What this means is that if you consider our scenario above where we have two datacenters and two CAS Array’s CAS1 and CAS2 we can control the cross-site failover event.  In the event where Cross Site Connections are allowed the RPCClientAccessServer remains CAS1 and CAS1 will connect the user to their mailbox server in Datacenter 2.  However, say we wish to disable Cross Site Connections, in the event of a failover Autodiscover detects the profile change and updates the client to point to CAS2 (requires restart).  CAS2 then will provide the mailbox access to the mailbox server in Datacenter 2!  This behavior in SP1 is based on three properties.Â
1.  Home server property in Outlook
2. Preferred database site (RPCClientAccessServer)
3. Active database site

Now, keep in mind that since the Autodiscover service is being used this feature will not work well with Outlook 2003.  Actually during one of the session it was strongly encouraged that if you are still using Outlook 2003 you should move off of it prior to moving to Exchange 2010.  In the event that you have disabled Cross Site Connections and have outlook 2003 when outlook attempts to connect to CAS1 it will detect the failover via ecWrongServer and redirect to CAS2.  However, in the event that CAS1 goes down, Outlook 2003 can’t update if the source CAS goes down.

Don’t ask me how to configure, that part wasn’t convered and I haven’t had a chance to play with SP1 in a lab yet.  

Hope you enjoyed this article, I will continue to work on getting more for everyone!  Have a great night!