  We present results from our cosmological N-body simulation which consisted of
2048x2048x2048 particles and ran distributed across three supercomputers
throughout Europe. The run, which was performed as the concluding phase of the
Gravitational Billion Body Problem DEISA project, integrated a 30 Mpc box of
dark matter using an optimized Tree/Particle Mesh N-body integrator. We ran the
simulation up to the present day (z=0), and obtained an efficiency of about
0.93 over 2048 cores compared to a single supercomputer run. In addition, we
share our experiences on using multiple supercomputers for high performance
computing and provide several recommendations for future projects.
