The networks used in clusters vary greatly based on the users' particular needs. The following are example networks (from a hardware perspective). The first example is an inexpensive Ethernet network for use in a small cluster (< 32 nodes). The second example is an Ethernet network with moderate bisection bandwidth.
In Figure 4.1, we show a simple cluster network, consisting of a single switch and 8 cluster nodes. This is probably the most common network configuration for clusters. The performance is generally governed by a combination of network link speed, and aggregate backplane bandwidth of the switch.
Figure 4.1: A simple cluster network.
In Figure 4.2, we show a slightly more complicated cluster network, consisting of two switches and 16 cluster nodes evenly distributed across the switches. The performance of this configuration is dependent on more factors than the previous example. In this case, it is limited by a combination of link speeds, backplane bandwidth of both switches, and the effectiveness of the hashing algorithm used to aggregate the 4 uplinks between switches. This may seem like a similar performance limit to the previous example, but in these multi-stage switch networks, single switch limitation are aggregated non-linearly based on system usage.
Figure 4.2: A complex cluster network.