Hard & Soft Mount

This is a UNIX terminology as to what the client does when
it can't talk to an NFS Server. If you just mount a file
system without specifying hard or soft, the default is a
hard mount. Hard mounts are preferable because of the
stateless nature of NFS. If a client sends an I/O request to
the server (such as an ls -la), and the server gets
rebooted, the client will wait until the server comes back
on line. This preserves data transfers in the event of a
server failure. There are disadvantages to this, as a simple
mount request could hang. A soft link will return with an
error and fail. This kills the wait time, but can cause
problems with data transfers. 

Hard mount 
--
If the NFS file system is hard mounted the NFS daemons will try
repeatedly to contact the server. The NFS daemon retries will not time
out will affect system performance and you cannot interrupt them.
 
Soft mount 
-- If the NFS file system is soft mounted NFS will try repeatedly to contact the server until either: 
A connection is established 
The NFS retry threshold is met 
The nfstimeout value is reached