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BaBar Experience

BaBar Experience. Tim Adye Rutherford Appleton Laboratory PPNCG Meeting Brighton 11 th September 2002. Talk Outline. New (more distributed) BaBar computing model and its impact, especially on RAL User experience Transfers SLAC -> RAL Transfers UK -> SLAC. New Computing Model.

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BaBar Experience

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  1. BaBar Experience Tim Adye Rutherford Appleton Laboratory PPNCG Meeting Brighton 11th September 2002 Tim Adye

  2. Talk Outline • New (more distributed) BaBar computing model • and its impact, especially on RAL • User experience • Transfers SLAC->RAL • Transfers UK->SLAC Tim Adye

  3. New Computing Model • Goal is to spread computing load much more around the collaboration • Simulation production is already highly distributed • Small-scale analysis already performed atUniversities (9 in UK) and Regional Centres (eg. RAL) • Now have three new “Tier A” centres • Lyon – Objectivity (database) analysis (since last year) • RAL – Kanga (ROOT MicroDST) analysis (from May 02) • Padova – Reprocessing (commissioning) • RAL has relieved SLAC of all Kanga analysis • Each site requires large data transfers from and to SLAC Tim Adye

  4. BaBar CPU Usage at RAL Tier A Tim Adye

  5. User Experience • Now have users throughout US and Europe • Interactive experience is generally excellent • “Connecting to RAL and working at RAL was very fast, as fast as at SLAC.” – Uriel Nauenberg, University of Colorado at Boulder. • AFS access between UK and SLAC is still slow • SLAC -> RAL AFS, RAL+UK -> SLAC AFS • Maybe an intrinsic property of AFS with slower RTT Tim Adye

  6. Bulk transfers SLAC->RAL • Production at SLAC has come in bursts • Reprocessing old data • Kanga production is the final (and relatively simple) step in a long processing chain • We have had no problem keeping up with steady state • Sometimes delays of 1-2 weeks to catch up with a burst in production • This is quite acceptable • So far, >19 TB copied from SLAC and on disk at RAL • 15 TB since January • RAL is now the primary Kanga repository, so others in UK/Europe/US will copy from us • So far modest: most << 1TB per site (10-20 sites) Tim Adye

  7. Kanga Data transfersbbftp SLAC->RAL Tim Adye

  8. Transfer Rateper bbftp session (2-20 streams each) Tim Adye

  9. Bandwidth • Transfer rate of 5-25 Mbit/s is obviously much less than SLAC<->RAL 622 Mbit/s link • Actually get up to 50 Mbit/s by using multiple sessions (on different servers) • Probably several effects limit us • Only run a few (1-5) simultaneous sessions • More is cumbersome to manage • Currently use only a couple of 100 Mbit/s servers at RAL • Firewall problems with bbftp limit servers we can use • Will soon have dedicated import/export Gbit servers • bbftp doesn’t handle small files very efficiently • Typical file sizes 10-500 MB • Will use bbcp, but requires a bug fix (on Andy’s list) • Not a problem at the moment Tim Adye

  10. Transfers UK->SLAC • UK now performs ~75% of total BaBar Simulation Production • Mostly at University sites, though RAL is starting up • Objectivity output files sent back to SLAC • Size reduced by a factor of 8 after dropping intermediate files • no longer required for most analysis • Output then skimmed, converted, and re-exported to Tier A and C sites Tim Adye

  11. By site 20 TB 140 TB Transferred To SLAC ! 10 TB 8 TB Raw/sim not sent @SLAC since Apr02 rate drop: x8 By week 4 TB 1 Sep 02 1 Aug 01 Simulation Transfers to SLAC (all sites)

  12. UK Simulation ProductionA typical UK site • Transfer rate limited by local+SLAC infrastructure and number of bbftp streams (currently 3) • Gaps in transfers show we are keeping up – CPU is main limit Full plots athttp://www.ep.ph.bham.ac.uk/user/smith/ Transfer rate Tim Adye

  13. Summary • New computing model is heavily reliant on network • Especially UK to/from SLAC • User experience is good • but is there anything we can do about AFS? • Bulk transfer from and to SLAC currently limited by local infrastructure • Nevertheless, we are easily keeping up with SLAC and UK farm production Tim Adye

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