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A Look At CERN's LHC Grid-Computing Architecture
blair1q writes "Using a four-tiered architecture (from CERN's central computer at Tier 0 to individual scientists' desk/lap/palmtops at Tier 3), CERN is distributing LHC data and computations across resources worldwide to achieve aggregate computational power unprecedented in high-energy physics research. As an example, 'researchers can sit at their laptops, write small programs or macros, submit the programs through the AliEn system, find the necessary ALICE data on AliEn servers, then run their jobs' on upper-tier systems. The full grid comprises small computers, supercomputers, computer clusters, and mass-storage data centers. This system allows 1,000 researchers at 130 organizations in 34 countries to crunch the data, which are disgorged at a rate of 1.25 GB per second from the LHC's detectors."
As someone who worked on the processing of HEP experimental data for awhile, let me say that there is a ton of work to do. You have particles entering the detector every ~40ns and hundreds of different instruments making measurements, which leads to a ton of data very quickly. You then have to reconstruct the path of the particle based off of the detector information, but it's not straight-forward. The detector can have gaps in coverage; neutrinos (which are undetectable) can be created removing momentum; particles from the previous event can still be in the detector et cetera.
And all of the data crunching you do must be done in 40ns, so that you're ready for the next set. (Of course, you can do some processing offline, but if you don't maintain a 40ns average, then your data will start piling up.)
Have a look here: http://lcg.web.cern.ch/LCG/image.htm for Google Earth based dashboards showing WLCG live grid sites, links, data transfer and job activity.