Troubleshooting NFS

Adding an NFS volume from ESX:
esxcfg-nas -a <datastore name> -o <nfs servername or ip> -s <mount point>
esxcfg-nas -l   list NFS volumes

Adding an NFS volume from VCLI:
vicfg-nas.pl --server <esx hostname> --add nfsshare --nasserver <ip/dns name> --share <mount point>

NFS logs :
ESX --->\var\log\vmkernel
ESXi--->\var\log\messages
cat \var\log\vmkernel | grep nfs

Troubleshooting steps for NFS :
1) Refresh the storage
2)Check VMkernel is configured correclty
3)Verify firewall ports UDP/TCP 111 & 2049 are open
4)Verify NFS client is open in Security profile/firewall
5) Test connectivity -vmkping from esx to nas server
6) Verify share & permissions on NAS server
7)Check the messages or vmkernel log file

References :
Vmware KB 1003967