  A status report is presented on the large-volume simulations in the
Schroedinger functional with two flavours of O(a) improved Wilson quarks
performed by the ALPHA collaboration. The physics goal is to set the scale for
the computation of the fundamental parameters of QCD. In this talk the emphasis
is on aspects of the Hybrid Monte-Carlo algorithm, which we use with
(symmetric) even-odd and Hasenbusch preconditioning. We study the dependence of
aucorrelation times on the trajectory length. The latter is found to be
significant for fermionic correlators, the trajectories longer than unity
performing better than the shorter ones.
