So one of the biggest misunderstandings I run into is related to DAGS and availability of the databases. Often times people ask why is their databases offline after a failover to another site. And even the same question may come up when patching.

It is important to understand quorum. And honestly I think most people do. the challenge is many seem to think the File share witness or alternate file share witness will come into the mix when it really won’t let me try to explain.

In order to have quorum we have to have an odd number of votes in a cluster. So in order for us to have an odd number of votes there are multiple ways a cluster can be configured (this is done under the covers on exchange) you can have Node Majority. or Node file share majority. So what is the difference?

With Node majority only the Nodes are counted no file share witness is used. Yes you may have specified it. but for vote count it is not used. So lets say you have a 3 Node DAG. the cluster will say Node majority

If I eject the node it will show “Node and File Share Majority”

So what does this really mean. Well in 3,5,7,9,11,13,15 Node DAG’s the file share witness does not play a role or count for a Vote.

In 2,4,6,8,10,12,14,16 Node DAG’s the file share witness will act as a vote. Some will say a deciding vote that is a little misleading. Fact is you have to have Quorum. so the FSW can be offline if enough Nodes are available to maintain Majority things will be fine. this is why it is called “Node And File share Majority”

Hope this helps someone have a great day.