observing the vmkernel log 5 mins and the results at bellow :
tail -f vmkernel.log
2013-01-25T13:12:45.282Z cpu0:4104)WARNING: NFS: 221: Got error 13 from mount call
2013-01-25T13:13:15.284Z cpu6:4102)WARNING: NFS: 221: Got error 13 from mount call
2013-01-25T13:13:45.288Z cpu4:6079)WARNING: NFS: 221: Got error 13 from mount call
2013-01-25T13:14:15.291Z cpu6:6079)WARNING: NFS: 221: Got error 13 from mount call
2013-01-25T13:14:45.295Z cpu5:4101)WARNING: NFS: 221: Got error 13 from mount call
2013-01-25T13:15:15.298Z cpu6:4102)WARNING: NFS: 221: Got error 13 from mount call
2013-01-25T13:15:45.301Z cpu6:4102)WARNING: NFS: 221: Got error 13 from mount call
2013-01-25T13:16:15.305Z cpu5:6079)WARNING: NFS: 221: Got error 13 from mount call
2013-01-25T13:16:45.307Z cpu6:6076)WARNING: NFS: 221: Got error 13 from mount call
2013-01-25T13:17:15.311Z cpu2:6106)WARNING: NFS: 221: Got error 13 from mount call