Name	E_mail_Address	Scientific_Session	Contribution_type	Title	Authors_affiliations	Abstract	
Groen / Derek	djgroen@science.uva.nl	EAS Symp.6:Dynamics of Galaxies and Galactic Nuclei.	oral	Distributed N-body Simulation on the Grid Using Dedicated Hardware	Derek Groen/Universiteit van Amsterdam (SCS & API), Simon Portegies Zwart/Universiteit van Amsterdam (SCS & API), Alessia Gualandris/Rochester Institute of Technology and Steve McMillan/Drexel University	We present performance measurements of direct gravitational N-body simulation on the
grid, with and without specialized (GRAPE-6) hardware. Our inter-continental virtual-organization
consists of three sites, one in Tokyo, one in Philadelphia and one in Amsterdam. We run simulations
with up to 131072 particles for a variety of topologies. As expected, high performance simulations
over the entire planet are dominated by network latency. Based on these timings we construct
a model to predict the performance of a hypothetical grid consisting of all the 582 GRAPE-6
modules on Earth. Such setup reaches break-even between network communication and computation
for N \' 108 particles, resulting in a compute time of about one year for 1 N-body time unit.
Much better performance can be obtained using only a local cluster of GRAPEs. Equipping the
Netherlands DAS-3 grid with GRAPEs would achieve break-even at a million particles, resulting in
a compute time of about half an hour for 1 N-body time unit.