Why is an unmounted Exchange Server hosting mailboxes after having configured a DAG but haven't brou

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I have 2 exchange 2010 ent. servers. both have HT, CA, Mailbox roles installed on them and I have a witness server with out the mailbox role.

So I haven't gotten the green light for network downtime to bring the DAG online. So today I decide to take down the 2nd exchange server that has no mounted DBs and all of sudden I have 4 end-users (out of 100) telling me that their mailboxes are disconnected and that their MB's are looking to connect to this second exchange server....why???

Thanks for any and all help!


Alexei Segundo

Do you have a load-balanced CAS array? It sounds like those 4 users were probably connected to the CAS on the server that went down and were not automatically redirected to the working CAS. Remember that in E2010 MAPI clients connect to the CAS and not directly to the mailbox database.Alexei


Thanks Alexei for the quick reply. I have not configured a CAS array. I just read that I can't use windows NLB on the DAG servers b/c of issues with failover clustering being used..what's an alternative. I'm wondering if I can install the NLB on the witness server and then configure the CAS array via cmdlet..thoughts??

Heather B.

Brian Day MCITP

If a CAS Array is not configured before DBs are created then a random CAS server is chosen as the RpcClientAccessServer attribute. It sounds like the DB those users aer on chose the CAS service on the server you rebooted as the RpcClientAccessServer attribute.

You can always configure a CAS Array object, then put an A record in DNS for the FQDN of the CAS Array that just points to one CAS server for now until you get a load balancing mechanism in place, then change the A record to point to the LB VIP at a later time.

Microsoft Premier Field Engineer, Exchange
MCSA 2000/2003, CCNA
MCITP: Enterprise Messaging Administrator 2010
Former Microsoft MVP, Exchange Server
My posts are provided "AS IS" with no guarantees, no warranties, and they confer no rights.


Ok gotcha..but can I just use my witness server for the NLB??Heather B.

Alexei Segundo

> Ok gotcha..but can I just use my witness server for the NLB??

No, the NLB members need to be the CAS servers themselves. NLB is incompatible with Windows Failover Clustering (required for DAG), so if you want LB your only option is to use a hardware LB (or split out the CAS role onto different servers and then use NLB).



Thanks Alexei. What's the minimum amount of servers you need to have a DAG?Heather B.

Alexei Segundo

Hi Heather

Three is the minimum for a DAG, e.g. two servers hosting the mailbox role and 1 hosting the File Share Witness.



Ok I get that and have that scenario but I guess what I don't get is that it doesn't provide fail over clustering in terms of when one is offline like it did for me ...it didn't shift to the online server..

Sorry for all the questions and confusion on my part but from this minimum cofiguration you're saying that it wouldn't load balace, correct?

Thanks for all your help.

Heather B.
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