bWatch is a GUI Beowulf Cluster Monitor. It displays load averages, memory, swap, number of processes and users for all nodes in a single window. bWatch is available from http://www.sci.usq.edu.au/staff/jacek/bWatch.
One way of obtaining statistics from your beowulf cluster is via httpd
running on your server node, and a CGI script. The idea is that the
CGI script executes remote shells to the node your are querying, and
formats the retrieved information into a HTML page which the httpd
server sends to your browser. This is a very easy way of checking the
system performance from anywhere in the world as long as there is a
browser and an Internet connection. There is an example
index.html file at
ftp://ftp.sci.usq.edu.au/pub/jacek/beowulf-utils which calls
the CGI script getinfo.cgi.
Netpipe is a very good network performance testing tool which enables to check the throughput of TCP, MPI, and PVM of different size packts. You can use gnuplot or a spreadsheet to plot the results produced by Netpipe's. You can find NetPIPE at http://www.scl.ameslab.gov/Projects/ClusterCookbook/nprun.html