When you configure NFS servers to work with ESXi, follow recommendation of your storage vendor. In addition to these general recommendations, use specific guidelines that apply to NFS in vSphere environment.
The guidelines include the following items.
Make sure that the NAS servers you use are listed in the VMware HCL. Use the correct version for the server firmware.
Ensure that the NFS volume is exported using NFS over TCP.
Make sure that the NAS server exports a particular share as either NFS 3 or NFS 4.1. The NAS server must not provide both protocol versions for the same share. The NAS server must enforce this policy because ESXi does not prevent mounting the same share through different NFS versions.
NFS 3 and non-Kerberos (AUTH_SYS) NFS 4.1 do not support the delegate user functionality that enables access to NFS volumes using nonroot credentials. If you use NFS 3 or non-Kerberos NFS 4.1, ensure that each host has root access to the volume. Different storage vendors have different methods of enabling this functionality, but typically the NAS servers use the no_root_squash option. If the NAS server does not grant root access, you can still mount the NFS datastore on the host. However, you cannot create any virtual machines on the datastore.
If the underlying NFS volume is read-only, make sure that the volume is exported as a read-only share by the NFS server. Or mount the volume as a read-only datastore on the ESXi host. Otherwise, the host considers the datastore to be read-write and might not open the files.