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A Look At CERN's LHC Grid-Computing Architecture 53

Posted by Soulskill
from the going-for-the-gusto dept.
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."
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A Look At CERN's LHC Grid-Computing Architecture

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  • I wonder when we will have the equivalent computing power at home? :)

    • Re: (Score:1, Funny)

      by Anonymous Coward

      According to Moore's Law.. about 4 Hitlers away

      Damn thats Godwins.. Moore's says about 12 years.

    • I wonder when we will have the equivalent computing power at home? :)

      When you will create a black hole at home. Simple !!!

    • Your post makes me wonder about a future where I have a home computer powerful enough to run an algorithm which downloads as many tracks off of iTunes as it needs and then can compute by extrapolation the future hits of RIAA, before they are released.

      One wonders whether the courts would find that such a program is a circumvention of DRM for the purposes of the DMCA. Unfortunately, the computer, which can answer that question, will be destroyed by the construction of a .....

      (Ouch. I should go get some sleep.

    • ...I already do! One of the great things about the LCG is that you can submit and monitor jobs from anywhere. It is used by far more than the 1,000 physicists the article mentions. There are 2,500+ on ATLAS alone and then there is CMS and LHCb to count as well.
  • by Goldsmith (561202) on Saturday May 15, 2010 @10:40AM (#32219532)

    I was having lunch with some CERN guys a couple weeks ago, and was asking them about the speed of their analogue to digital converters. I don't remember what the number was, but it seemed low to me, something like 200kHz. So, of course, I had to point out that *my* cheapo converters ran faster than theirs by more than an order of magnitude. They responded with "well, each of our converters does 200kHz on all of our 4000 channels at the same time, so we're really recording at..."

    They won.

    • It depends on which CERN guys you talk to. When I was a grad student we had a 1 GHz ADC (with fewer channels and only 8 bits IIRC) reading out scintillator which timed protons in a beam to O(10ps) timing resolution. I've been more involved with triggers than front end digitization since then but 200 kHz and 400 channels is nothing - the ATLAS calorimeter alone has 110,000 channels and its ADC's operate in the 10's MHz range (IIRC - you'd have to look up the ATLAS detector paper for exact numbers).
      • by Goldsmith (561202)

        You know, I don't really remember the exact numbers we were talking about at lunch. I'm sorry if I got some of the numbers wrong, particularly if they ended up being far to small, that would annoy me.

        I just remember being very impressed at the insane amount of total data coming in. I'm definitely more used to the setup of a single GHz ADC, switching between a handful of channels.

        There's a big difference in scale between a condensed matter experiment, where I get to do absolutely everything myself, and som

  • by Anonymous Coward

    is a botnet !

    Thanks in advance.

    Yours In Akademgorodok,
    K. Trout

  • Good thing they didn't use PS3s to build [slashdot.org] it.
  • I was quite saddened to find that this 'Look at CERN's LHC GRID' ....didnt include any pictures. :-(

  • I just wish they would send some more work units down the LHC@Home pipe. None of my computers have done any work for that project in ages.

    -l

  • Correction (Score:3, Informative)

    by mike260 (224212) on Saturday May 15, 2010 @11:25AM (#32219822)

    Using a 4-tiered architecture (from CERN's central computer at Tier 0 to individual scientists' desk/lap/palmtops at Tier 3) [...]

    Sorry for being pedantic, but the article says there are three tiers between the central computer and the scientist's machines (which are tier 4, not 3).

    • Tier 0
      Tier 1
      Tier 2
      Tier 3
      • by mike260 (224212)

        And finally Tier 4 which comprises, according to TFA, the scientists desk/lap/palmtops.

        • by Arathrael (742381)

          Correct. Tier 3 is local batch farm facilities, etc., which aren't really part of the project as such.

    • by blair1q (305137)

      Interesting. I don't remember writing it that way. Did someone edit the submission before it was posted? Or has it just been a long weekend?

  • Data to crunch (Score:5, Interesting)

    by Lord Byron II (671689) on Saturday May 15, 2010 @11:27AM (#32219840)

    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.)

    • ...there is a ton of work to do ... which leads to a ton of data...

      Holy crap! I had no idea that the relativistic speeds involved would cause the mass to increase that much!

    • Re:Data to crunch (Score:5, Informative)

      by klazek (1134141) on Saturday May 15, 2010 @12:52PM (#32220492)

      You have particles entering the detector every ~40ns and hundreds of different instruments making measurements, which leads to a ton of data very quickly.

      Not exactly true. It's running at 40 MHz, so that's 25 ns bunch spacing. Further, you don't exactly have to 'crunch' the data as it comes in, there are multiple triggers that throw lots of data away based momentum cuts and other criteria before it ever makes out of the detectors.

      In ATLAS, for example, there are ~ 10e+9 interactions/sec. The Level1 Trigger, consists of fast, custom electronics programmed in terms of adjustable parameters to control filtering algorithms. Input is from summing electronics in the EM and hadron calorimiters, and signals from the fast muon trigger chambers. The info is rather coarse at this point (transverse momentum cuts, narrow jet criteria, etc), and at level one the info rate is decreased in about ~2us (including communication time), from 40MHz to about 75KHz. Level2 now does a closer look, taking more time and focusing on specific regions of interest (RoIs). This process takes about 10ms, and data rate is reduced to about 1KHz for sending to the event filter. Here, the full granularity of the detector (the 'detector means all the bits - Inner detectors: Pixels, strips, Transition Radiation tracker - The calorimiters - The muon tubes at the outside radius) and runs whatever selections algorithms are in use. This takes a few seconds, and output is reduced to about 100Hz and written to disc for a gazillion grad students (like myself) to analyze endlessly and get our PhDs.

      There is much more to it of course, but you can find info about it on line if you really are interested in the details. Have a look at the ATLAS Technical Design Report: http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/TDR/TDR.html [web.cern.ch]

  • by Anonymous Coward

    There was a good presentation at LISA '07 on this entitled "The LHC Computing Challenge":

    http://www.usenix.org/event/lisa07/tech/tech.html#cass

    It was given by Tony Cass, who is/was "responsible for the provision of CPU and data storage services to CERN's physics community". They're planning on collecting 15PB/year.

  • I wonder what they at cern were expecting to have for infrastructure at the end of the project (e.g. now).
    I mean: who could have guessed the processorspeed and diskspace we have now.

  • by imevil (260579) on Saturday May 15, 2010 @04:41PM (#32221916)

    I can say that the article doesn't explain it very well. Since CERN has been calling the sites "Tier", this terminology has become a buzzword, and everything is a Tier (the managers call their services "Tiered" just to make them sound important).

    Tier0 and Tier1 are well described by the article. Tier2 are mostly computing clusters, with of course big storage, but they're mainly for analysis. Tier3 are like Tier2 but not really. They are "uncertified" Tier2 in the sense that they do not strictly adhere to the Tier2 standards in terms of middleware and configuration and policies.

    Tier4... never heard of that, I think the buzzword Tier backfired and they're calling their desktops Tiers. When I started managing the Tier3 we did not even call it like that... it was just a cluster.

  • Imagine a Beowulf cluster of these! \o/

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