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LHC experiments Requirements and Concepts ALICE

LHC experiments Requirements and Concepts ALICE. LEP in 1989. … and in 2000. Outline. ALICE general description Requirements Architecture Software Data Challenges. Two running modes. Dr Jekyll… Pb-Pb collisions general-purpose heavy ion experiment … and Mr Hyde pp beam

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LHC experiments Requirements and Concepts ALICE

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  1. LHC experimentsRequirements and ConceptsALICE

  2. LEP in 1989...

  3. … and in 2000

  4. Outline • ALICE general description • Requirements • Architecture • Software • Data Challenges

  5. Two running modes Dr Jekyll… • Pb-Pb collisions • general-purpose heavy ion experiment … and Mr Hyde • pp beam • large cross-section pp processes

  6. ALICE data rates Pb-Pb run pp run Trigger type Minimum Bias Central Dielectrons Dimuon NA 20 1 - 87 20 67 - 87 200 67 - 87 670 0.7 - 2.4 Event rate (Hz) Event size (MB) 500 2 1 0.5 0.1 Data in DAQ (GB/s) Data in EB (GB/s) Data on tape (GB/s) 24.5 2.5 1.25 1 month (106 s) 1 10 months 1 Run period Total on tape (PB)

  7. The original architecture

  8. Detector Data Link • Functions: • main interface with the detectors • handle detector-to-LDC data flow • handle LDC-to-detector commands & data • Keywords: • cheap • small • functional • rad-hard • long distance • optical • used everywhere

  9. Local Data Concentrator • Functions: • handle and control the local DDL(s) • format the data • perform local event building • allow monitoring functions • ship events to the event builders (GDCs) • Keywords: • distributed • good data moving capabilities • from the DDL • to the Event Building Link • CPU power not indispensable • Not a farm

  10. Global Data Collector • Functions: • accept the data sent from the LDCs • perform final event building • ship the events to the Permanent Data Storage (PDS) • Keywords: • distributed • good data moving capabilities • from the LDCs • to the PDS • CPU power not indispensable • farm

  11. Event Destination Manager • Functions: • collect availability information from the GDCs • distribute event distribution policies to the data sources • Keywords: • optimized network usage • look ahead capabilities

  12. Event Building Link • Functions: • Move data from the LDCs to the GDCs • Keywords: • big events (1-3, 67-87 MB) • low rates (20, 500, 670 Hz) • many-to-many • mainly unidirectional

  13. Overall key concepts • Keep forward flow of data • Allow back-pressure at all levels (DDL, EBL, STL) • Standard Hw and Sw solutions sought: • ALICE collaboration • CERN computing infrastructure • Whenever possible go COTS • During the pp run, keep any unused hardware busy

  14. Mismatch of rates • Recent introduction of: • Transition Radiation Detector (TRD) • Dielectron trigger • change in Pixel event size • increase in estimated TPC average occupancy • Required throughput an order of magnitude too high! • New scenarios: • region-of-interest readout • online compression • online reconstruction • introduction of a level 3 trigger

  15. The new architecture

  16. The Event Building process • Events flow asynchronously into the LDCs • Each LDC performs - if needed - local event building • The Level 3 farm - if present - is notified • Level 3 decision - if any - is sent to LDCs and GDC • All data sources decide where to send the data according to: • directives from the Event Destination Manager • the content of the event • The chosen GDC receives: • sub-events • optional reconstructed and compressed data • optional level 3 decision • The Event Building Link does the rest

  17. Software environment DATE • Data acquisition environment for ALICE and test beams • Support DDLs, LDCs, GDCs and liaison to the PDS • Standalone and complex DAQ systems • Integrated with HPSS and CASTOR (via CDR) • Keywords: • C • TCP/IP • Tcl/Tk • Java • ROOT

  18. Data challenges • Use state-of-the-art equipment for real-life exercise • 1998-1999: Challenge I • 7 days @ 14 MB/s, 7 TB • 1999-2000: Challenge II • 2 * 7 days @ max 100 MB/s, > 20 TB • transfer simulated TPC data • 23 LDCs * 20 GDCs (AIX/Solaris/Linux) • with offline filtering algorithms and online objectifier (ROOT) • two different MSS (HPSS and CASTOR) • several problems  limited stability

  19. Data Challenge II

  20. Event building network Pure Linux setup 20 data sources FastEthernet local connection GigaBit Ethernet backbone

  21. Run log

  22. Data Challenge III • Will run during the winter 2000-2001 shutdown • Target: 100 MB/s (or more) sustained over [7..10] days • Improved stability • More “ALICE like” setup • abandon older architectures still in use at the test beams • Implement 10% of the planned ALICE EB throughput • Integrate new modules & prototypes: • improved event building • Level 3 • Regional Centers • Will use the LHC computing testbed • Better status reporting tools: use PEM if available

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