11gR2 : Do not allow to use nfs as ocr and vote disk in aix6l ?

AIX 6L : # oslevel -s
6100-05-06-1119
#
Storage : QNAP TS-809U   ---- NAS Storage
on AIX configure iSCSI get disk
# lsdev -Cc disk
hdisk0 Available 06-08-00 SAS Disk Drive
hdisk1 Available          Other iSCSI Disk Drive            --iSCSI disk
hdisk2 Available          Other iSCSI Disk Drive            --iSCSI disk
hdisk3 Available          Other iSCSI Disk Drive            --iSCSI disk
hdisk4 Available          Other iSCSI Disk Drive            --ISCSI disk
#
use NFS install 11gR2 grid
dd if=/dev/zero of=/orafs/ocr/ocrfile1 bs=268435456 count=1        --256MB
dd if=/dev/zero of=/orafs/ocr/ocrfile2 bs=268435456 count=1
dd if=/dev/zero of=/orafs/ocr/ocrfile3 bs=268435456 count=1

then in [Storage Option Information] window select Shared File System