NFS server not responding/is alive again

[Janos Dohanics]

I have a FreeBSD 4.11 machine which mounts a volume from a Netapp ONTap.
The FreeBSD machine also acts as a Samba PDC. The Samba volumes are in
the NFS-mounted volume. There are about a dozen Win2K workstations on
the network served by the Samba server.

Lately I have noticed that /var/log/messages is full with entries like:

... /kernel: nfs server filer01:/vol/vol0/psa: not responding
... /kernel: nfs server filer01:/vol/vol0/psa: is alive again

It seems that the server sometimes is unresponsive for less than a
second, many other times it's unresponsive for a number of seconds (as
many as 8 seconds).

This happens quite frequently, sometimes 60+ times an hour, perhaps not
surprising that it doesn't happen or happens rarely when the
workstations are not being used.

There are also 15-20 "got bad cookie" messages per day.

The NFS volume is mounted with rw,-r=1024.

I have looked at some nfsstat output, but I don't know what if anything
should I be looking for there.

Is this a FreeBSD or an ONTap problem? What can I do to fix it?