  We review large scale modelling of the ISM with emphasis on the importance to
include the disk-halo-disk duty cycle and to use a dynamical refinement of the
grid (in regions where steep variations of density and pressure occur) for a
realistic modelling of the ISM. We also discuss the necessity of convergence of
the simulation results by comparing 0.625, 1.25 and 2.5 pc resolution
simulations and show that a minimum grid resolution of 1.25 pc is required for
quantitatively reliable results, as there is a rapid convergence for Delta x
\leq 1.1 pc.
