  The architecture of several data centers have been proposed as alternatives
to the conventional three-layer one.Most of them employ commodity equipment for
cost reduction. Thus, robustness to failures becomes even more important,
because commodity equipment is more failure-prone. Each architecture has a
different network topology design with a specific level of redundancy. In this
work, we aim at analyzing the benefits of different data center topologies
taking the reliability and survivability requirements into account. We consider
the topologies of three alternative data center architecture: Fat-tree, BCube,
and DCell. Also, we compare these topologies with a conventional three-layer
data center topology. Our analysis is independent of specific equipment,
traffic patterns, or network protocols, for the sake of generality. We derive
closed-form formulas for the Mean Time To Failure of each topology. The results
allow us to indicate the best topology for each failure scenario. In
particular, we conclude that BCube is more robust to link failures than the
other topologies, whereas DCell has the most robust topology when considering
switch failures. Additionally, we show that all considered alternative
topologies outperform a three-layer topology for both types of failures. We
also determine to which extent the robustness of BCube and DCell is influenced
by the number of network interfaces per server.
