Because of these limits, CERN cannot cope with all the data coming from the experiments. Thus, it has set up the LCG (LHC Computing Grid) Project to build and maintain a data-storage and analysis infrastructure for the entire high-energy physics community who work with the LHC. It will give roughly 15,000 scientists in some 500 research institutes and universities worldwide access to experimental data. Further, data must be available over the 15-year estimated lifetime of the LHC. The analysis of the data, including comparison with theoretical simulations, requires of the order of 100,000 CPUs at 2006 measures of processing power.

CERN chose a data grid model because it provides several key benefits. For one, the significant costs of maintaining and upgrading the necessary resources for such a computing challenge are more easily handled in a distributed environment. Also, there are fewer single points of failure.

A distributed system also presents significant challenges which include ensuring adequate levels of network bandwidth, maintaining coherence of software versions at various locations, coping with heterogeneous hardware, managing and protecting data so it is not lost or corrupted, and providing accounting mechanisms so that different groups have fair access.

CERN has dubbed itself as the Tier0 computing facility, and it sends all the data to Tier1 facilities, of which there are roughly a dozen such as Fermilab and the Grid Computing Center in Karlsruhe, Germany. A requirement for the Tier0 and all Tier1 facilities is that they must be available 24 hours a day, seven days a week. A full copy of all the experimental data is spread across all the Tier1 facilities.

Tier1 centres make subsets of data available to Tier2 centres, each consisting of one or several collaborating computing facilities that can store sufficient data and provide adequate computing power for specific analysis tasks. There are approximately 200 to 300 Tier2 centres.

Finally, individual scientists can access even smaller subsets of data from particular experiments through Tier3 computing resources, which can consist of local clusters in a university computer centre or even individual PCs. The Tier3 centres are just now being set up, so there are no hard numbers of the users. But a rough guess of all the computing nodes that will be used from Tier0 through Tier3 is in the order of 30,000.