The Scalability of the Cluster-Booster Concept - A critical assessment of the DEEP architecture

Cluster computers are dominating high-performance computing (HPC) today. The success of this architecture is based on the fact that it profits from the improvements provided by mainstream computing well known under the label of Moore's law. But trying to get to Exascale within this decade might require additional endeavors beyond surfing this technology wave. In order to find possible directions for the future we review Amdahl's and Gustafson's thoughts on scalability. Based on this analysis we propose an advanced architecture combining a Cluster with a so-called Booster element comprising of accelerators interconnected by a high-performance fabric. We argue that this architecture provides significant advantages compared to today's accelerated clusters and might pave the way for clusters into the era of Exascale computing. The DEEP project is implementing this concept. Six applications from fields having the potential to exploit Exascale systems are being ported to DEEP. We analyze one application in detail and explore the consequences of the constraints of the DEEP systems on its scalability