Hello!

According to this https://technet.microsoft.com/en-us/library/dd979790%28v=exchg.150%29.aspx

"Datacenter Activation Coordination (DAC) mode is a property of a database availability group (DAG). DAC mode is disabled by default but should be enabled for all DAGs with two or more members that use continuous replication."

I've never had any problems with switchovers/failovers for my two-member DAG with this option (DAC) disabled.

I'd like to understand if DAC is so valuable option why it's disabled by default? Should I (or any other Exchange administrator) enable it right after creating a DAG in any case or there could be any additional considerations?

Thank you in advance,

Michael

Hello Michael,

It is very explained here (http://exchangeserverpro.com/datacenter-activation-coordination-mode/).

Thanks.

Hello Sunny Kewalramani,

Thank you for the article, but it just illustrates what's been written in MSDN concerning multi-site DAG.

Regarding single-site DAGs it just says "It can also occur in a single-site DAG in some network failure situations. "  and the main questions - what are these "failure situations" and are these situations worth enabling DAC are still unanswered...

Regards,

Michael

• Edited by MF47 17 hours 21 minutes ago

How is your DAG configured?

For example, two nodes and a FSW?

I think it would be difficult to have that condition with 3 nodes and no alt FSW.

Just thinking about it for a moment. 

Hello Sunny Kewalramani,

Thank you for the article, but it just illustrates what's been written in MSDN concerning multi-site DAG.

Regarding single-site DAGs it just says "It can also occur in a single-site DAG in some network failure situations. "  and the main questions - what are these "failure situations" and are these situations worth enabling DAC are still unanswered...

Regards,

Michael

• Edited by MF47 Thursday, March 26, 2015 2:04 PM

Yes, two nodes and FSW.

Well, I suppose if you had an alternate FSW in a routed network, with DAG node 1 and the FSW on one subnet and DAG node 2 and the alt FSW on another subnet AND...

If routing failed

AND...

If someone reset DAG node 2 to use the alt FSW (not realizing the real problem has to do with network connectivity)

AND THEN...

routing started to work again...

Maybe then you could create the scenario in a single Active Directory site.

Yes, I surmised as much...

Thank you very much, David!

Regards,

Michael