ATLAS Muon data quality with 2010 LHC

ATLAS is a large multipurpose detector, presently in the full operational phase at LHC, the CERN Large Hadron Collider accelerator. The ATLAS Muon Spectrometer has been designed to provide standalone measurement of the muon momentum up to a few TeV with a relative precision better that 10% and to trigger on single muons with transverse momentum down to a few GeV, and an efficiency close to 100%, taking into account the high level background environment, the inhomogeneous magnetic field, and the large size of the apparatus (24 m diameter by 44 m length). ATLAS MS detector has being commissioned using all types of physics data available: cosmic rays and events produced during a few days of LHC single beam operations. This first year of data taking has been of great interest, not only for the physics outcome, but also for operating the system under the environment it was designed for. This paper is describing the design, the implementation as well as the data quality performance achieved during this first year of data taking. We also describe how to reduce the cosmic background contamination in early collisions data.