Evaluation of Link Failure Resilience in Multirail Dragonfly-Class Networks through Simulation

During long-term operation of a high-performance computing (HPC) system with thousands of components, many components will inevitably fail. The current trend in HPC interconnect router linkage is moving away from passive copper and toward active optical-based cables. Optical links offer greater bandwidth maximums in a smaller wire gauge, less signal loss, and lower latency over long distances and have no risk of electromagnetic interference from other nearby cables. The benefits of active optical links, however, come with a cost: an increased risk of component failure compared with that of passive copper cables. One way to increase the resilience of a network is to add redundant links; if one of a multiplicity of links between any two routers fails, a single hop path will still exist between them. But adding redundant links comes at the cost of using more router ports for router-router linkage, reducing the maximum size of the network with a fixed router radix. Alternatively, a secondary plane of routers can be added to the interconnect, keeping the number of compute node endpoints the same but where each node has multiple rails of packet injection, at least one per router plane. This multirail-multiplanar type of network interconnect allows the overall size of the network to be unchanged but results in a large performance benefit, even with lower-specification hardware, while also increasing the resilience of the network to link failure. We extend the CODES framework to enable multirail-multiplanar 1D-Dragonfly and Megafly networks and to allow for arbitrary link failure patterns with added dynamic failure-aware routing so that topology resilience can be measured. We use this extension to evaluate two similarly sized 1D-Dragonfly and Megafly networks with and without secondary router planes, and we compare their application communication performance with increasing levels of link failure.