NFS, process hung in disk wait state

[Kent Adams]

I have recently upgraded from 4.0 to 4.1 using the 4.1 upgrade kit.
I believe we have an NFS problem, but cannot determine the cause.
Support have not been overly helpful yet.
We have a DECstation 5000 which exports user directories via NFS
to two DS3100's and a DS2100.  One of the 3100's serves mail,
news and local software.  Both start 8 nfsd and 5 biod daemons.
The 5000 has 32MB, the 3100 24MB both with bufcache 15.

The problem manifests itself when a particular user cannot
access his directory from the 3100 and gets a process in a
D state.  The user, unaware of the problem may login again,
do the same command and so on until he has several processes
in a D state.  This may affect a couple of users but does not
affect all.  Neither the user nor root can kill these
processes.  The only clearance is achieved by a reboot.

Has anyone had similar problems?  Is this a 4.1 problem or my
configuration.  It didn't happen under 4.0.
-- 
Regards, Kent Adams     Internet:cckba at marlin.jcu.edu.au
Phone:+61 77 814255     Snail:  Computer Centre
  Fax:+61 77 796371             James Cook University
                                Townsville..4811