John, thanks for your answer, I think I'm looking for a hihg performance cluster with two pcs... Apache, Mailscanner/Postfix, mysqld and squid are going to run in this cluster..

Each of those apps has its own requirements for a shared workload cluster. frankly, I have no idea how a squid cluster could or would work.

webservers like apache are most frequently clustered by being put behind a load balancing router such as BigIP from F5. this is $$$$$$.

mysql has its own clustering support, I'm not very familiar with it. typically, these require shared storage.

not sure why you'd need to cluster a mail server other than high availability, this typically requires shared storage for the spool files and such.

I have no idea how you'd loadbalance cluster a squid cacheing proxy between two systems with discrete SATA drives. maybe if the squid cache was stored on a NFS server?

frankly, with that workload, and the hardware resources you described, you'd probably get the best performance by balancing the applications across the two systems. whichever app requires the most resource, put it on one, put the rest on the other. if the 'other' is overloaded, move another task to the first.