Last year more than 20 sites of NorduGrid operated as a single resource to contribute about 30% of the total Data Challenge 2 (DC2) for the ATLAS experiment, which will run at CERN's Large Hadron Collider (LHC). This was the first attempt to harness large amounts of strongly heterogeneous resources in various countries for a single collaborative exercise using Grid tools.

NorduGrid has participated in the ATLAS Data Challenges since August 2002, and was the first Grid system to contribute to LHC computing in a production mode. NorduGrid develops, maintains and supports an open-source Grid middleware known as the Advanced Resource Connector (ARC). ARC consists of the Grid services running on the computing resources, an indexing service for resources and data, and clients making intelligent use of the distributed information and data available on the Grid. Since its first release in 2002 the ARC middleware has run without interruption, growing from its initial five sites to 50 sites today in 10 countries: Australia, Denmark, Estonia, Finland, Germany, Norway, Slovakia, Slovenia, Sweden and Switzerland.

For the ATLAS DC2, production was split across three Grid "flavours": Grid3 (in the US), LHC Computing Grid (LCG) and NorduGrid/ARC. The exercise lasted half a year and processed 10 million events in more than 300,000 jobs. Apart from providing data for the researchers, testing software, and validating the ATLAS computing model, DC2 demonstrated the interoperability between different Grid flavours at the application level.

Although originally designed to provide resources for ATLAS computing, NorduGrid has served many other sciences. It was first employed by theory groups, and today the infrastructure is used in many fields, ranging from biomedical sciences and pharmacology to climate modelling and space physics.

NorduGrid provides middleware for several national Grid projects, and will soon supply its middleware for a cross-Nordic Grid facility. DC2 proved that ARC can operate reliably in a heterogeneous environment, and, since it is free open-source software, interest is growing outside its Nordic cradle. Groups in Iceland, Latvia, Lithuania, Sri Lanka and Russia are involved in partnership projects with NorduGrid participation.

Compiled by Hannelore Hämmerle and Nicole Crémel