The Large Hadron Collider at CERN near Geneva is the largest scientific instrument on the planet. When it begins operations, it will produce roughly 15 Petabytes (15 million Gigabytes) of data annually, which thousands of scientists around the world will access and analyse.

The data from the LHC experiments will be distributed around the globe, according to a four-tiered model. A primary backup will be recorded on tape at CERN, the “Tier-0” centre of LCG. After initial processing, this data will be distributed to a series of Tier-1 centres, large computer centres with sufficient storage capacity and with round-the-clock support for the Grid.

The Tier-1 centres will make data available to Tier-2 centres, each consisting of one or several collaborating computing facilities, which can store sufficient data and provide adequate computing power for specific analysis tasks.

Individual scientists will access these facilities through Tier-3 computing resources, which can consist of local clusters in a University Department or even individual PCs, and which may be allocated to LCG on a regular basis.