For the third year of the Ohm Project (9/2002-8/2003), we will reconfigure Ohm to use a hypercube-star hybrid topology. More precisely, the interconnect for our 16 server nodes will be reconfigured to form a 4-dimensional hypercube, so that each server is directly connected to four 'neighbors'. The following diagram depicts this topology, with the new network links shown in red, the 'master' nodes shown in light blue, and the 'server' nodes shown in dark blue:

To implement this topology, we add two more network interface cards (NICs) to each node, supplementing the NICs used in year 1 and year 2, for a total of five NICs/node. Each node's routing tables are also reconfigured so that:

• packets to a node's first neighbor in the hypercube are directed to the NIC for that neighbor,
• packets to a node's second neighbor in the hypercube are directed to the NIC for that neighbor,
• packets to a node's third neighbor in the hypercube are directed to the NIC for that neighbor,
• packets to a node's fourth neighbor in the hypercube are directed to the NIC for that neighbor, and
• packets to any other node are directed to the NIC for the switch.

After collecting performance data in this configuration for six months, we will finalize the cluster's topology. At this time, regular maintenance of the cluster will begin, so that the cluster's hardware is updated every three years.