famous last words!
NFS just stopped today!
All hosts had the export mounted, and just lost access to datastores.
Checking NFS 4.1 not responding, nothing in any of the logs as to why./
Trying to stop and start NFS hangs. All networking is fine and okay, no jumbo frames and this is on the older 1GBe.
So the initial problem we were trying to solve, has returned.
No access was being performed to the storage.