ATLAS Computing: From Commissioning to 7TeV Data

In this paper we summarise ATLAS operations from the STEP09 campaign in June 2009 through to ATLAS taking data in the first 7 TeV collisions at the LHC in 2010. We describe the lessons which were learned from the STEP09 challenge, both in proving which parts of the system were in good shape, but also in highlighting those areas which required improvement. We then describe the experience of ATLAS computing operations during the first LHC data taking era. The ATLAS experiment has successfully recorded, reconstructed, distributed and analysed millions of collision events delivered by the LHC at an unprecedented centre-of-mass energy of 7 TeV. The involved large-scale data processing operations, both the prompt reconstruction at Tier0 and the subsequent reprocessing campaigns in the Tier1 sites in the Grid, worked remarkably well.