  The Cosmic Dark Ages and the Epoch of Reionization constitute a crucial
missing link in our understanding of the evolution of the intergalactic medium
and the formation and evolution of galaxies. Due to the complex nature of this
global process it is best studied through large-scale numerical simulations.
This presents considerable computational challenges. The dominant contributors
of ionizing radiation were dwarf galaxies. These tiny galaxies must be resolved
in very large cosmological volumes in order to derive their clustering
properties and the corresponding observational signatures correctly, which
makes this one of the most challenging problems of numerical cosmology. We have
recently performed the largest and most detailed simulations of the formation
of early cosmological large-scale structures and their radiative feedback
leading to cosmic reionization. This was achieved by running extremely large
(up to 29 billion-particle) N-body simulations of the formation of the Cosmic
Web, with enough particles and sufficient force resolution to resolve all the
galactic halos with total masses larger than 10^8 Solar masses in computational
volumes of up to (163 Mpc)^3. These results were then post-processed by
propagating the ionizing radiation from all sources by using fast and accurate
ray-tracing radiative transfer method. Both of our codes are parallelized using
a combination of MPI and OpenMP and to this date have been run efficiently on
up to 2048 cores (N-body) and up to 10000 cores (radiative transfer) on the
newly-deployed Sun Constellation Linux Cluster at the Texas Advanced Computing
Center. In this paper we describe our codes, parallelization strategies,
scaling and some preliminary scientific results. (abridged)

Astrophysics