This question has popped up various times now, how does vSphere recognize an NFS Datastore? This concept has changed over time and hence the reason many people are confused. I am going to try to clarify this. Do note that this article is based on vSphere 5.0 and up. I had a similar article a while back, but figured writing it in a more explicit way might help answering these questions. (and gives me the option to send people just a link :-))
When an NFS share is mounted a unique identifier is created to ensure that this volume can be correctly identified. Now here comes the part where you need to pay attention, the UUID is created by calculating a hash and this calculation uses the “server name” and the folder name you specify in the “add nfs datastore” workflow.
This means that if you use “mynfserver.local” on Host A you will need to use to use the exact same on Host B. This also applies to the folder. Even “/vols/vol0/datastore-001” is not considered to be the same as “/vols/vol0/datastore-001/”. In short, when you mount an NFS datastore make absolutely sure you use the exact same Server and Folder name for all hosts in your cluster!
By the way, there is a nice blogpost by NetApp on this topic.