My home ESXi box is running low on storage, so it was time to start looking at keeping some files on the Unraid NAS.
Now, the NAS is never going to be super fast, so rather than store live VMDKs on there, the idea is to use it as a store for my ISO files, of which I have built up quite a collection.
So first things first - lets enable NFS in Unraid through Settings - Network Services - NFS

Now go to Shares and select an existing share and you should see an NFS section. Set the Export value to Yes, and set Security to Public (as this is an internal deployment and it's only me using it).

Click Apply and you are all done at the NAS end.
Hop on over to the ESXi 6 management web console, right click on the Storage title in the left menu and select New datastore.

Select Mount NFS datastore, and on the following screen enter the connection details.
Name: Name that you wish the ESXi server to know the datastore as
NFS server: The IP address or FQDN of the Unraid NAS
NFS share: /mnt/user/<name of the share on the NAS> (you can ssh onto the NAS and do a ls -l /mnt/user to double check)
NFS version: NFS 3 (as we are not using username and password) otherwise NFS 4

Click next and you will be shown a confirmation, so click Finish and you should be all set up. You may need to refresh the Datastores tab on the ESXi web front end just to display it.
Easy!