contribs.org/smeserver.org currently runs on a 5 node hardware cluster with 18 xen domU instances hosting different aspects of the site. Each node has a quad 2.6Ghz processor and 16GB ram. All nodes connect back to a 13TB raid-6 + 1 spare iscsi box and is backed up daily to a 26TB AIT-3 library. Critical parts of the cluster are also mirrored offsite to two different locations (mysql realtime sync, all other parts rsync every 12 hours).