DAG Failover Testing

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DG1212

I've configured a DAG with two servers that have the CAS/HT/MB server roles. When I go ahead and disable the NIC on the primary Ex server (to test the DAG failover functionality) the databases automatically mount on the secondary Ex server just fine. The issue I'm having is that once the DB's mount on the secondary server, Outlook is unable to open users mailboxes. They get " the server is unavailable" message. Do I need a CAS array in order for Outlook client to look for the secondary CAS server once a DAG failover event takes place?
 
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pantherfan69

Yes, since you have all the roles on each box, the cas servers arent load balanced. You would want to seperate the cas roles into a cas array and use a load balancer for them. You also have to make sure that both mailbox servers point to a cas array rather than an individual cas server for HA.
 
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DG1212

The secondary server is only for HA. I don't think I would need a load balancer in that serious...correct?

Shouldn't the autodiscover service automatically point any Outlook clients to the secondary Exchange server without needing a CAS array?
 
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pantherfan69

each mailbox server is associated with either a specific cas server, or a cas array " shared" name. Since you have all roles on each server, you cant run windows network load balancing to load balance requests in case of failover to the cas array because it cant be loaded on the same machine as a mailbox server running in a DAG (since the dag uses failover clustering).

you can either seperate the cas roles on new servers and run windows network load balancing, or create an " alias" name that the cas servers are registered for (and which you have a certificate matching the name for), and manually in dns change the ip address of that alias based on which cas server you want them to use. I dont think that is a recommended way to do it though

the other method would be a hardware load balancing device in front of the cas servers to deal with the problem.
 
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Allen Song

Hi,

The mailbox database is associated with the CAS under the RPCClientAccessServer attribute which provides the access for the Outlook 2007 clients.

The RPCClientAccessServer is the same in the Active and Passive database. Thus, it's still using the original CAS after failover the database.

To workaround this issue, you should load blance the CAS or point the IP address to the second CAS manually.

Thanks

Allen

Allen Song
 
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