We have a 4 node availability group with 3 node on the primary data center and one node on the secondary data center.
We want to add a file share witness and since we dont have a third data center and not allowed to go with cloud witness, where would the file share witness be ? At the primary or secondary.
Will putting on the secondary helps as the majority of the nodes are in the primary data center
For this setup it technically matters but in the end it really won't. The long and the short of it is it should be at your primary site since that has 75% of all resources.
Why it doesn't technically matter is that there would need to be enough loss at the primary side that having the witness at the secondary datacenter would be helpful. If there was that amount of loss then generally the cluster would need to be forced up (there are ways this wouldn't be required). In the event of losing communication between both sites then in every case (except some vary timing specific edge cases) the secondary side would never even be in the running for a majority so it's kind of moot.
