Distributed Computing Grid Experiences in CMS DC04

In March-April 2004 the CMS experiment undertook a Data Challenge (DC04). During the previous 8 months CMS undertook a large simulated event production. The goal of the challenge was to run CMS reconstruction for sustained period at 25Hz input rate, distribute the data to the CMS Tier-1 centers and analyze them at remote sites. Grid environments developed in Europe by the LHC Computing Grid (LCG) and in the US with Grid3 were utilized to complete the aspects of the challenge. A description of the experiences, successes and lessons learned from experiences with grid infrastructure is presented.