  Redshifted 21cm measurements of the structure of ionised regions that grow
during reionization promise to provide a new probe of early galaxy and
structure formation. One of the challenges of modelling reionization is to
account both for the sub-halo scale physics of galaxy formation and the regions
of ionization on scales that are many orders of magnitude larger. To bridge
this gap we first calculate the statistical relationship between ionizing
luminosity and Mpc-scale overdensity using detailed models of galaxy formation
computed using relatively small volume - ($\sim$100Mpc/$h$)$^{3}$, high
resolution dark matter simulations. We then use a Monte-Carlo technique to
apply this relationship to reionization of the intergalactic medium within
large volume dark matter simulations - ($>$1Gpc/$h$)$^{3}$. The resulting
simulations can be used to address the contribution of very large scale
clustering of galaxies to the structure of reionization, and show that volumes
larger than 500Mpc/$h$ are required to probe the largest reionization features
mid-way through reionization. As an example application of our technique, we
demonstrate that the predicted 21cm power spectrum amplitude and gradient could
be used to determine the importance of supernovae feedback for early galaxy
formation.
