Static Allocation of Multirail Networks

Using multiple independent networks (also known as rails) is an emerging technique to overcome bandwidth limitations and enhance fault-tolerance of current high-performance clusters. This report presents the limitations and performance of static rail-allocation approaches, where each rail is pre-assigned a direction for communication. An analytical lower bound on the number of networks required for rail allocation is shown. We present an extensive experimental comparison of the behavior of various allocation schemes in terms of bandwidth and latency, compared to static rail allocation. We also compare the ability of static and dynamic rail-allocation mechanism to stripe messages over multiple rails. Scalability issues of static and dynamic rail allocation are also compared. We find that not only static rail allocation necessarily consumes many resources, it also performs poorly compared to dynamic rail allocation schemes, in all the tested aspects.