This is taken from Red Hat Portal How to create an export domain or iso domain? (Need customer access)

On the NFS, you need to do the following

# mkdir /export/data
# chown -R 36:36 /export/data
# chmod 755 /export/data
# vim /export_data
/export/data *(rw)
# /etc/init.d/nfs restart
# chkconfig nfs on

The key setup is that the ownership must be given vdsm kvm (36:36). Or you will have errors like
“Error while executing action Add Storage Connection: Problem while trying to mount target”

# mkdir /export/ISO 
# chown -R 36:36 /export/ISO 
# chmod 755 /export/ISO 
# vim /export/ISO /export/ISO *(rw) 
# /etc/init.d/nfs restart 
# chkconfig nfs on

References:

1. Red Hat Enterprise Virtualisation and NFS (NetApp Community)
2. How to create an export domain or iso domain? (Red Hat Portal – Restricted Access)