[imp] single machine versus load balancing

[Charlie Reitsma]

I am running Apache 2.0.44, PHP 4.3.1, Horde 2.2.1, Imp 3.2.1 and Turba
2.1 on a Sun Netra X1, 500MHz single processor with 1 Gig RAM on Solaris
8. Preferences, sessions and contacts are stored in MySQL on the same
box as the web server. The IMAP server is a separate box. This is a
campus of 2100 students and 650 staff; the population size does not
change much.

Using the rule that active sessions contain 's:3:"imp";b:1;' in the
session_data our usage ranges from 70 to 1700 with an average of 800 
sessions.

setoolkit reports the CPU is overloaded (I'll see load average over 50
sometimes). Users will experience a minute between clicks sometimes. The
IMAP box rarely exceeds 50%. The high load is http clients.

Reading the scaling article on the horde site I get the feeling that
there are sites handling my population size on a single box without
problems. Should I consider load balancing with round-robin DNS or a
dual processor single box? That is, do the advantages or disadvantages
of either choice make one more desirable?

If I were to go a single box I probably would go with a Sun LX50, dual
processor, 1 Gig RAM running Solaris. If I were to do load balancing I 
would continue to use Sun Netra X1 and look at load balancing hardware 
as well.

TIA,
Charlie