Challenges of the LHC Computing Grid by the CMS experiment

This document summarises the status of the existing grid infrastructure and functionality for the high-energy physics experiment CMS and the expertise in operation attained during the so-called ”Computing, Software and Analysis Challenge” performed in 2006 (CSA06). This report is especially focused on the role of the participating computing centres in Germany located at Karlsruhe, Hamburg and Aachen. In preparation for the enormous amounts of data expected from the future large hadron collider (LHC) presently under construction at the European laboratory for particle physics, CERN, a grid infrastructure is being set up by the physics communities in the participating countries. The world-wide LHC Computing Grid (WLCG) is based on tier-structured layers of one Tier0 at CERN and several Tier1, Tier2 and Tier3 centres distributed all around the globe. The German part of the CMS grid infrastructure relies heavily on the two Helmholtz centres Forschungszentrum Karlsruhe as Tier1 and DESY Hamburg as well as on installations at the universities Karlsruhe and Aachen. The emphasis of this report lies on so-called service challenges performed in 2006 where the full functionality of the whole chain from data processing at the Tier0, data distribution to the Tier1 and Tier2 centres up to organised data re-processing and more chaotic physics analyses by single users was exercised.