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ALICE Data Challenges

ALICE Data Challenges. Fons Rademakers. Data Challenge. When fully operational ALICE will take data with a rate of 1.5 GB/s An order of magnitude higher than any of the other LHC experiments Since we are unique we can not piggyback on ATLAS/CMS/IT R&D. Objectives.

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ALICE Data Challenges

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  1. ALICE Data Challenges Fons Rademakers

  2. Data Challenge • When fully operational ALICE will take data with a rate of 1.5 GB/s • An order of magnitude higher than any of the other LHC experiments • Since we are unique we can not piggyback on ATLAS/CMS/IT R&D

  3. Objectives • Simulate the ALICE on-line and off-line data recording and processing chain • Track technologies: • DATE, ROOT, MSS, networking, CPU's and OS'es • Repeat frequently to collect data points to see if we will be ready for 1.5 GB/s in 2005 Be ready for T=0 with as little surprises as possible

  4. First Data Challenge • To store 10TB of raw data in a ROOT DB on HPSS within 5 days (i.e. 25 MB/s) • To test the following technologies: • DATE, ROOT, HPSS, GB ethernet, Linux and PC's • Very simple event model, but fairly realistic raw, tag and catalogue database environment • Executed in March 1999

  5. ADC1 Data Flow Computer center NA57 Data source Intel/Linux PC PowerPC/AIX ROOT objectifier LDC pipe GDC Event Builder 5 MB/s switch GB eth rfcp LDC 5 MB/s disk GB eth DATE = LDC+GDC 5 MB/s HPSS RS6000/AIX 5 node cluster

  6. DATE Data Source • DATE is developed by the ALICE DAQ team and used by NA57 and COMPASS • See talk by R. Divia (B293) this afternoon • LDC = Local Data Concentrator • GDC = Global Data Collector • In this setup the LDC's generated bit patterns simulating (NA57) events (size 400 - 500 KBytes/event)

  7. RAW Data DB • Raw data DB contains AliEvent objects, which contain: • an AliEventHeader object • 16 data members (72 bytes) • an AliRawData object • char array (variable length, 400-500 kB) • AliEvent objects are stored in a single TTree container with two branches (for the two contained objects)

  8. RAW Data DB (cont.) • No compression (need more CPU power) • Size of individual raw DB's typically between 250 MB and 1.5 GB (tunable parameter) • As soon as a raw DB is closed it is moved to HPSS via rfcp (part of CERN SHIFT software interfaced to HPSS)

  9. Tag DB • Tag DB contains AliEventHeader objects, which contain: • size, type, run number, event number, burst number, trigger, time, detector id, etc. • AliEventHeader objects are stored in a single TTree with 16 branches (one for each header data member) • Compressed • Stays on disk • Used for fast event selection

  10. Run Catalog DB • Run DB contains one AliStats object per produced raw data DB • An AliStats object contains: • filename of raw DB, number of events, begin/end run number, begin/end event number, begin/end time, file size of raw DB, compression factor, quality histogram (TH1F) • Compressed • Stays on disk • Used for matching run/event with raw DB

  11. This was one of the largest OODB's in HEP !

  12. NA57 Data source Computer center 9 PowerPC/AIX LDC Intel/Linux PC Cluster 5 MB/s LDC Switch Event Filter 5 MB/s GDC Event Builder GB eth ROOT objectifier Switch Pipe 5 IntelPC/Linux 10 MB/s LDC Switch GB eth 10 MB/s LDC 10 MB/s Catalog Tag DB HPSS/ CASTOR MSS Alice DAQ Lab Data source DATE = LDC+GDC 20 node cluster

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