Cool... I understand better now :)
What we decided to do here, at Greenpeace, is to use several uniprocessor machines for the webservers. Each machine has 512MB of RAM -even though now it seems cheap enough to have 1GB of RAM- and SCSI 10Krpm HDD's.These machines are HP and have been running as webservers for more than 260 days without need to reboot (redhat 7.3). Pentium III 800MHz. We are currently serving peaks of 16 hits/sec per machine during one hour and the load is quite noticeable, the CPU is really busy :)
Another way could be to go the SMP way, have a dual (or quad) processor machine to handle AOLServer, then you don't have the problems when trying to syncronize the cache among the different machines.
This work from Philip Greenspun, Eve Andersson and Andrew Grumet
might give you some ideas on SMP vs Single Proc. We decided to go the single processor way because it's easier to add more simple machines that look the same when the load goes up.
We have had quite good experience with Dell so far, running RedHat Linux (5.x, 6.x, 7.x and now 8.0). I have been using a Dell 2500 for quite some time now with a hardware RAID card. Nice and fast but it's working as a database server.
Hope this helps ...
BTW all this wasn't for dotLRN but just openACS + custom code