Distributed Availability group with witness server for quorum

Question

I have experience in setting up availability group and have used witness server when the nodes are even to achieve quorum.

One of the vendor provided a layout which will have two availability group across two data centers and distributed availability group will be used.

Online resources also does not mention anything about a witness server among the two availability group.

Here is my question since each ag's will have even number of nodes and if there are no witness server how will the cluster survive during patching if one node goes down.

Answer 1

Here is my question since each ag's will have even number of nodes and if there are no witness server how will the cluster survive during patching if one node goes down.

Each side will be a different cluster, each with their own quorum. Quorum is at the cluster level, and is generally required for AGs to come online, since the cluster will not bring resources online if it does not have quorum.

Thus, you should set each cluster's configuration appropriately for high availability in terms of witness choices. Note that since Windows Server 2012R2 there is dynamic witness and dynamic quorum which are both enabled by default (and depending on version can't be disabled).