ATLAS Distributed Computing Monitoring tools after full 2 years of LHC data taking

This paper details variety of Monitoring tools used within the ATLAS Distributed Computing during the first 2 years of LHC data taking. We discuss tools used to monitor data processing from the very first steps performed at the Tier-0 facility at CERN after data is read out of the ATLAS detector, through data transfers to the ATLAS computing centers distributed world-wide. We present an overview of monitoring tools used daily to track ATLAS Distributed Computing activities ranging from network performance and data transfers throughput, through data processing and readiness of the computing services at the ATLAS computing centers, to the reliability and usability of the ATLAS computing centers. Described tools provide monitoring for issues of different level of criticality: from spotting issues with the instant online monitoring to the long-term accounting information.