ATLAS detector data processing on the Grid

The ATLAS detector is in the second year of continuous LHC running. A starting point for ATLAS physics analysis is data reconstruction. Following the prompt reconstruction, the ATLAS data are reprocessed, which allows reconstruction of the data with updated software and calibrations providing coherence and improving the quality of the reconstructed data for physics analysis. The large-scale data reprocessing campaigns are conducted on the Grid. Computing centers around the world participate in reprocessing providing tens of thousands of CPU-cores for a faster throughput. Reprocessing relies upon underlying ATLAS technologies providing reproducibility of results, scalable database access, orchestrated workflow and performance monitoring, dynamic workload sharing, and petascale data integrity control. These technologies are also empowering ATLAS physics and subsystem groups in further data processing steps on the Grid. We present the experience of large-scale data reprocessing campaigns and group data processing on the Grid.