  Recent work has shown that expander-based data center topologies are robust
and can yield superior performance over Clos topologies. However, to achieve
these benefits, previous proposals use routing and transport schemes that
impede quick industry adoption. In this paper, we examine if expanders can be
effective for the technology and environments practical in today's data
centers, including the use of traditional protocols, at both small and large
scale while complying with common practices such as over-subscription. We study
bandwidth, latency and burst tolerance of topologies, highlighting pitfalls of
previous topology comparisons. We consider several other metrics of interest:
packet loss during failures, queue occupancy and topology degradation. Our
experiments show that expanders can realize 3x more throughput than an
equivalent fat tree, and 1.5x more throughput than an equivalent leaf-spine
topology, for a wide range of scenarios, with only traditional protocols. We
observe that expanders achieve lower flow completion times, are more resilient
to bursty load conditions like incast and outcast and degrade more gracefully
with increasing load. Our results are based on extensive simulations and
experiments on a hardware testbed with realistic topologies and real traffic
patterns.
