Exchange 2010

We have a two node stretched DAG. A CAS-HT Server and a mailbox server in the main office and another CAS-HT server and mailbox server in the data center. A file share witness server is set up on CAS-HT in main office and alternate file share witness server is set up in the DR site.
We want to patch CAS-HT server in the main office. Would taking CAS-HT server down in the main office cause the DAG to failover to the DR site ? Or could the cas-ht server which is also a witness server can be patched and rebooted without affecting the DAG?
We dont want the DAG to failover to the DR site when rebooting the cas-ht server which is also the FSW.
We are aware that Outlook clients will loose connectivity once CAS-HT server gets rebooted.

Thanks.
abhi1024Asked:
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Adam FarageEnterprise ArchCommented:
A file share witness server is set up on CAS-HT in main office and alternate file share witness server is set up in the DR site.

....

We want to patch CAS-HT server in the main office. Would taking CAS-HT server down in the main office cause the DAG to failover to the DR site ? Or could the cas-ht server which is also a witness server can be patched and rebooted without affecting the DAG?

No, you would be fine DAG wise.

Lets say this is your setup:

Primary Site -
CAS/HT-01 (primary-vote)
MBX-01(primary-vote)

DR Site -
CAS/HT-02
MBX-02 (primary-vote)

If the Primary FSW is located on CAS/HT-01 but MBX-01 / MBX-02 stay online (because you are patching CAS/HT-01), you still have a quorum. Although the databases will not go offline as you have 2/3 votes, connections to MBX-01 (e.g: mailbox users) will not be processed as there is no CAS within the local site that is available. This is normal, and once the CAS/HT-01 come back online then you are OK.

As long as two of the three votes (see above) stay online the DAG will not fail, but remember if you have a single CAS within the site no mailbox connections will be servered to it until a local CAS within that site is available (CAS/HT-2 will not proxy directly to MBX-02, its just the way Exchange works).

Now you might be asking yourself "why is there no vote for CAS/HT-02", and that is because the Alternative FSW (A-FSW) will not be counted as a vote unless you are doing a datacenter switchover..http://technet.microsoft.com/en-us/library/dd351049%28v=exchg.141%29.aspx
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