mounting namenode dir on remote NFS Server

make a directory of your choice on the server: 
mkdir /var/hdfs/dfs 

export it in /etc/exports, giving the IP address of your NN: 
/var/hdfs/dfs 10.1.2.3(rw,no_subtree_check) 

refresh your exports: 
exportfs -a 

log into the NN and verify the export is visible: 
showmount -e nfsserver.example.com 

Export list for nfsserver: 
/var/hdfs/dfs * 

make the local mount point and mount it: 
mkdir -p /mnt/nfs/dfs 
mount nfsserver.example.com:/var/hdfs/dfs /mnt/nfs/dfs 

Now mention this dir :/mnt/nfs/dfs  in your hdfs-site.xml