Datacenter Activation Coordination (DAC) mode is a property setting for a database availability group (DAG).
DAC mode is disabled by default and should be enabled for all DAGs with 2 or more members that use continuous replication.
That means the majority of Exchange DAG deployments need the DAC mode.
The DAC is most useful in a multi-datacenter configuration to prevent split brain syndrome, a condition that occurs when all networks fail, and DAG members can’t receive heartbeat signals from each other.
However, I suggest you always enable the DAC.
If you enable the DAC and you need to recover, the recovery takes less commands on the command line. Only the following commandlets will be necessary:
Also, if you did NOT enable the DAC, you cannot do so if you have a failure. The DAC must be enabled ahead of time.
Here is how to enable the DAC mode:
1. Go to Exchange Management Shell
2. Type the following, where DAG2 is your DAG name:
Set-DatabaseAvailabilityGroup -Identity DAG2 -DatacenterActivationMode DagOnly
For more information, read this article:
Here is the session slide deck:
Pictured here is Alexis St. Clair, who won the Nest programmable thermostat raffle. The Nest was offered by my company CDI, the sponsor of the event, along with VMware and EMC.
Twitter Chat for remaining questions:
March 12, 2014, Wednesday
2 pm to 3 pm EST
Use Hashtag #CDIVplex in your questions.
My presentation is called “Stretching VMware clusters across distances with EMC’s Vplex – the ultimate in High Availability.”
This session is for administrators and consultants looking to stretch their VMware clusters across 2 geographical sites for enhanced High Availability and Disaster Recovery. Readers will learn:
- Differences between High Availability and Disaster Recovery approaches.
- When to use VMware Stretched Clusters vs. VMware Site Recovery Manager.
- How to decrease your Recovery Time Objective across sites to under 5 minutes.
- Minimum storage, network and compute requirements for VMware Stretched Clusters.
- What is distributed storage and how it helps with VMware Stretched Clusters.
- What is EMC’s Vplex?
- How Vplex allows you to configure VMware Stretched Clusters.
- Best practices for VMware Stretched Clusters with EMC’s Vplex.