nfs server /home not responding

[Lucas Wang]

Hi experts,

We use NFS to store /home directory for users in our lab.
However, we occasionally get blocked from logging in because 
the automount daemon on a NFS client machine hangs. When
that happens, we get this error message on the NFS client machine
called "bucks" in its system logs:
Aug 24 10:53:40 bucks kernel: nfs server pid670 at bucks:/home: not responding

pid670 is the amd process.

Our NFS server(raptors) has the following configuration:
FreeBSD raptors.cs.ucla.edu 7.3-PRERELEASE FreeBSD 7.3-PRERELEASE #0: Tue Feb  9 12:59:50 PST 2010     root at raptors.cs.ucla.edu:/usr/obj/usr/src/sys/RAPTORS  amd64

And the client machine is configured as:
FreeBSD bucks.cs.ucla.edu 7.3-PRERELEASE FreeBSD 7.3-PRERELEASE #0: Tue Feb  9 20:47:50 UTC 2010     root at bucks.cs.ucla.edu:/usr/obj/usr/src/sys/BUCKS  amd64

Another thing I want to add is that several other NFS client machines
also hang from time to time. But they don't usually hang at the same time.
Even though rebooting can fix the problem once, we don't want it keep hurting us.

So any insights or suggestions will be greatly appreciated. Thanks a lot.

Regards,
- Lucas