ATLAS Data Challenge 2: A Massive Monte Carlo Production on the Grid

The study and validation of the ATLAS Computing Model started three years ago and will continue for few years in the context of the so-called Data Challenges (DC). DC1 was conducted during 2002-03; the main goals achieved were to set up the simulation data production infrastructure in a real worldwide collaborative effort and to gain experience in exercising an ATLAS wide production model. DC2 (from May until December 2004) is divided into three phases: (i) generate Monte Carlo data using GEANT4 on three different Grid projects: LCG, GRID3 and NorduGrid; (ii) simulate the first pass reconstruction of real data expected in 2007, and (iii) test the Distributed Analysis model. Experience with the use of the system in world-wide DC2 production of ten million events will be presented. We also present how the three Grid flavours are operated. Finally we discuss the first prototypes of Distributed Analysis systems.