I have a 2 node AOAG cluster (MSSQL2014), replicas are on a different subnet on different locations. There's no 3rd location. OS is Windows Server 2012R2. I was wondering: what is the best location for the fileshare witness. On the primary or on the secondary? How will dynamic quorum behave?
If there is no third location why bother with a witness at all. Assign voting so that the 'primary' has a vote, and the secondary doesn't. If the network link goes, cluster stays on the 'primary' and the AG stays up. If you keep voting such that each node has a vote, and the links go, then you are at the mercy of dynamic voting, and whichever node it chose to weight. In Windows Server 2012 R2 you can control this with the LowerQuorumPriorityNodeID property. You'll never have fully automatic failover here as there is no true independent witness.