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DELPHI experience

DELPHI experience. I left collaboration in 1997 so I won’t talk about data preservation but another costly effort Change of offline compute platform from IBM mainframe  RISC UNIX

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DELPHI experience

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  1. DELPHI experience • I left collaboration in 1997 so I won’t talk about data preservation but another costly effort • Change of offline compute platform from IBM mainframe  RISC UNIX • Caveat: this recollection covers a period 20 years ago and is reconstructed from my own notes and mails from that period. Any error is entirely mine…

  2. Compute platform • Up to ~1992 main computing platform @CERN was the IBM mainframe CERNVM • As a physicist one quickly learned about • VM/CMS, REXX, XEDIT • DAQ and production learned VAX VMS • All offline code cross-compiled and certified • YPATCHY with CARds and CRAdles to control the versioning and platform differences • DELPHI’s own farms in p8 and basement of bat27 was entirely VAX based, at least to begin with • But for normal physics analysis there were never enough VAX compute resources to motivate a serious take-up

  3. DELPHI offline in numbers • 16 sub-detectors • ~1Hz trigger rate, average event size 50kB, peak event size 200kB (1990) • Yearly total DST (Data Summary Tape) volume • 1989: 3x IBM 3480 cartridge • 1990: 38x • 1991: 146x • Source code was pretty FORTRAN 77 formatted for punch-card compatibility • Main packages • DELSIM: 0.5-1M of SLOC (DELPHI didn’t use Geant3) • DELANA: ~>1M SLOC

  4. Migrate to RISC/UNIX • Compute cycles on CERNVM were precious • If you wanted run >1hrs job • go to offline computing office and give your justification • Priority was given to: • Higgs search and Z0 resonance precision measurements • QCD studies (like mine) were queued behind  Strong motivation to seek for other resources

  5. Benchmark that convinced me 2x60 = 120 CPUs/event 2x38x24x60x60/55’000 119 CPUs/event

  6. Moving to RISC/UNIX • Core teams (~1993): • DELPHI • Alfonso Lopez-Fernandez (CERN) (later Gilbert Grosdidier) • D. M. Edsall (Iowa State University Ames HEP Group) • Luiz Mundim(LAFEX-CBPF/PUC) • O. Bärring (CERN) • CN (IT) SHIFT • Frédéric Hemmer • Christian Boissat • CN Public Login (+AFS): Tony Cass • Tasks • Create an attractive and reliable compute and storage resource • More for less ($/IBM cycle  $/Risc cycle) • Cross-compile and certify • Mirror production and analysis software repos • Nightly builds + tests • Facilitate migration (REXX sh, csh) • Write targeted user guides (UNIX, SHIFT, FATMEN, …) • User support, public presentations and publicity • Rough cost: • Hardware (provided by CN): negligible (probably ~10-2 x IBM) • People: DELPHI ~6 person years for the full migration • Dedicated efforts completed in ~1995-6. Daily tasks (support etc.) integrated with general offline activities

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