Close to 300 members of the WLCG collaboration attended a recent workshop at CERN. Those in attendence represented 27 countries and 86 sites. Image courtesy of Will Venters.

Processing data for the Large Hadron Collider, the next-generation particle accelerator under construction at CERN, Switzerland, is one of the driving forces for development of grid technology.

The task of processing the 15 petabytes of data the LHC is predicted to generate each year falls to the Worldwide LHC Computing Grid Collaboration, which recently met at CERN for a week-long workshop in preparation for the start-up of the LHC later this year.

“WLCG doesn’t have its own grid,” explained WLCG’s Jamie Shiers. “It uses grids from several different projects. We use two major grid infrastructures: EGEE in Europe, and OSG in the United States, as well as many individual research centers. That we can get more than 200 sites to work together is really impressive.”

Shiers coordinates the WLCG service and runs the WLCG “service challenges.” These challenges stress the capacity and reliability of WLCG’s service to ensure it will be able to cope with the needs of the LHC experiments.

“This workshop was the first addressing the full WLCG team,” he said. The sites which have agreed to contribute to LHC data analysis in the WLCG collaboration  are arranged in a number of ‘Tiers.’ CERN will serve as the ‘Tier-0’ site, which will collect and distribute data to twelve ‘Tier-1’ sites. Some 150 ‘Tier’ 2 sites will contribute to processing the data. This was the first workshop to address all of these ‘Tiers,’ allowing all the partners in the WLCG collaboration to discuss the challenges that face them in getting ready to start taking data.

“This workshop helps us to prepare for the dress rehearsals this summer, which will be end-to-end tests of all components.” These rehearsals will test the full chain of computing, from the trigger systems used by the LHC experiments to record collisions  through to distributing the data and performing analysis around the globe.

Organizers designed the workshop to be highly interactive. “In previous workshops it was mostly just presentations,” said Shiers. “This time we wanted a more motivational event. Jos Engelen, CERN’s Chief Scientific Officer, gave a talk on LHC physics, not just the Higgs boson. We also organized a visit to the ATLAS detector. Many people had been told how big it was, but it’s a different scale from what most people imagine.” For many members of the collaboration this meeting was their last chance to see the detectors before the experiments close this summer in preparation for the start up of the LHC.

“There will be a pilot run of the LHC starting in November this year,” said Shiers. “As far as the WLCG service is concerned, we won’t be perfectly ready but we’ll be ready enough. We all need the pilot run, as there is a limit as to what we can do in testing. There will be some pain but I don’t foresee major problems, it will certainly be a busy year!”

- Owen Appleton, EGEE
iSGTW Contributing Editor