The GERmanium Detector Array (GERDA) is a neutrinoless double beta decay experiment in the Laboratori Nazionali del Gran Sasso (LNGS) and directly addresses the question of the Dirac or Majorana nature of neutrinos and their absolute mass scale. GERDA is specifically designed to test the currently pending claim of the Heidelberg Moscow Collaboration within its first phase of data taking which is soon to commence. The commissioning phase which started in July 2010 already reached a background level better than Heidelberg-Moscow, but remains by the time of April 2011 above the design goal. Initially, an unexpectedly large background contribution from ⁴²K was discovered, which became the major subject of investigation during the commissioning.