1. LHC collisions rate: 10 7 -10 9 Hz New PHYSICS rate: 0.00001 Hz Event selection: 1 in 10,000,000,000,000 Signal/Noise: 10 -13 Raw Data volumes produced by the LHC collisions and stored for further PHYSICS analysis: 2010: ~15 PetaBytes 2011: ~20 PetaBytes For the ALICE, ATLAS, CMS and LHCb experiments at the Large Hadron Collider (LHC) at CERN, the accomplishment of scientific results would be impossible without a distributed computing infrastructure – the Worldwide LHC Computing Grid (WLCG). Data written to tape (GB/month): 2010-2011 Experience of the WLCG data management system from the first two years of the LHC data taking Dagmar Adamova, for the ALICE Collaboration

2. Worldwide resources 2 Today, WLCG MoU has 49 signatories, representing 35 countries WLCG Collaboration Status: Tier 0; 11 Tier 1s; 68 Tier 2 federations; >130 Tier-2s WCLG, by the numbers About 8 000 physicists use it 42 MILLION jobs were run in September 2011 260 000 available cores. 150 PB disk available worldwide 20% of the computing resources are at CERN 14 972 processors run at CERN 2.7 MW is the power consumption of the CERN computer centre 10 GIGABIT/S optical fiber links connect CERN to each of the 11 Tier-1 institutes There is close to 50 PB of stored data at CERN already from LHC Up to 600 MB/S of data is stored by the ATLAS and CMS experiments during proton-proton collisions. 4 GB/S of data is stored by the ALICE and CMS experiments during heavy ion collisions.

3. 3 Summary and outlook: The LHC Grid infrastructure has been built, tested and used for 10 years. This was happening with continuous upgrading using newly emerging technologies and under regular and repeated stress-testing. Experiments have developed truly distributed computing models. WLCG performance during the first two years of LHC running has been impressive and has enabled very rapid production of PHYSICS results. Significant numbers of people are doing analysis on the Grid (up to ~800 per experiment) One of the positive features not envisaged in the beginning is the extremely reliable and high throughput network. There will be future challenges like the use of multicores and other CPU types, use of virtualization and cloud computing. “The LHC computing environment will outlive the accelerator itself, but it will evolve along with technology and is likely to become very different over the next few years.. “ (Ian Bird, the WLCG project leader).