NFS problem

[S. Johnson]

I have 2 client systems that need to access a mail volume via NFS.  I 
believe it is an optimization/setup problem, but am unsure of what to try 
to resolve it.  Here's the setup:

Server 3 - NFS Server, redhat 8.0, exporting /users from a fiber channel 
array it hosts.  Mail is sent to and picked up to users home directories, 
so there is a lot of disk access happening with read and writes (4500 
users).  /etc/exports looks like this:

/db     192.168.1.0/255.255.255.0(rw,no_root_squash)
/isp    192.168.1.0/255.255.255.0(rw,no_root_squash)
/users  192.168.1.0/255.255.255.0(rw,no_root_squash)

For now, the main export I am concerned with is /users, however, all these 
partitions are on the same fiber channel raid and are still accessed by the 
clients.  Traffic on the other two shares in pretty minimal, but may still 
be a factor in overall performance of the system.

Servers 1 and 2 are configured to be able to run Postfix or courier-imap, 
and access the /users share from server 3 via NFS.  Here is the /etc/fstab 
the clients use:

server3:/db    /db    nfs bg,nfsvers=3,rsize=8192,wsize=8192 0 0
server3:/isp   /isp   nfs bg,nfsvers=3,rsize=8192,wsize=8192 0 0
server3:/users /users nfs bg,nfsvers=3,rsize=8192,wsize=8192 0 0

Servers 1 and 2 are able to mount and read the volumes fine when there is 
little or no traffic.  However, when you move either Postfix or 
Courier-imap services over to them, they eventually (after several hours) 
start to have NFS problems.  After a while, there will be hundreds of dead 
processes still hanging around and the load average skyrockets (200 or 
more).  The mounts to /users or the other two are not available.  Executing 
a df or mount command hangs your terminal.  Sometimes you can kill off 
processes and restart NFS services, other times it requires a reboot of the 
client and usually means doing it by powering off the machine because it 
hangs on the NFS processes and will not shut them down.

Is there a tried and true way to setup NFS between the server and clients 
that will support high volumes of traffic?  If anyone knows of a better way 
to setup things the client and/or server side, please let me know.

Thanks,

Sean Johnson