1. ATLAS Computing Requirements LHCC - 19 March 2007 1 ATLAS Computing Requirements for 2007 and beyond

2. ATLAS Computing Requirements LHCC - 19 March 2007 2 History l ATLAS computing requirements were first worked out in 2003- 2005, in preparation of the Computing TDR and the Computing Addendum to the M&O MoU l Given the shift in LHC start-up schedule, we revised all inputs to the Computing Model in Summer-Autumn 2006 nThe current numbers are based on the results of that revision l On the same timescale, we contributed to building the “megatable” of necessary bandwidths between all Tier-1s and Tier-2s nSome of the megatable inputs are constrained by unbalanced pledges of disk/CPU capacity by a few Tier-2s and cannot by definition match our top-down requirements nIn terms of other resources, it just illustrates how, if we were to use the imbalanced Tier-2s as pledged, they would affect the storage at the Tier-1s, and given such a use of the Tier-2s, what the Tier-1–Tier-2 traffic should be

3. ATLAS Computing Requirements LHCC - 19 March 2007 3 ATLAS Requirements for 2007 CPU (MSI2k)Disk (PB)Tape (PB) Tier-01.90.080.4 CAF0.80.20.06 Sum of Tier-1s3.22.21.5 Sum of Tier-2s2.31.30.0

4. ATLAS Computing Requirements LHCC - 19 March 2007 4 ATLAS Requirements for 2008 CPU (MSI2k)Disk (PB)Tape (PB) Tier-03.70.152.4 CAF2.11.00.4 Sum of Tier-1s18.19.97.7 Sum of Tier-2s17.57.70.0

5. ATLAS Computing Requirements LHCC - 19 March 2007 5 Evolution

6. ATLAS Computing Requirements LHCC - 19 March 2007 6 Ratio to Computing TDR (June 2005) NB: there was a mistake in the Tier-0/CAF CPU requirements for 2007 in the Computing TDR (subsequently corrected already in 2005): CPU for calibrations does not scale with the length of the data-taking period

7. ATLAS Computing Requirements LHCC - 19 March 2007 7 Observations on computing resources l Data storage requirements generally fall with reduced live-time (obviously) l CPU does not fall as much nCERN CPU determined by rate and calibration requirements nMore calibration and optimisation is needed for 2007 data l Higher than hoped simulation time per event l Tier-1s see significant reductions wrt earlier (C-TDR) estimates nCumulative effect of less data on reprocessing l Tier-2s see a small initial fall but are bigger after 2009 l There is an argument for spreading the gain and the pain with Tier-1s by introducing more flexibility in the model: nTier-1s can now produce simulated data when not fully busy with reprocessing l Resources to be provided in 2007 are based on the original agreement on the ramp-up slope (30% in 2006 and 70% in 2007 wrt 2008) nResources we had available in 2006 were <<30% of the nominal 2008 capacities… nAnd known acquisition plans for many Tier-1 centres fall far short of 70% of the 2008 capacities

8. ATLAS Computing Requirements LHCC - 19 March 2007 8 Megatable rate inputs l Disk space is the resource that limits our total computing capacity right now nThis is true for both Tier-1s and Tier-2s l We distribute RAW and 1st-pass processed ESD data to Tier-1s approximately according to their pledged DISK capacities nAfter removing the disk space for AODs (100 kB/event) nBNL in addition gets a full set of ESD data l Our data distribution model requires a coupling between Tier-1s nAs we keep 2 copies of the most recent version of ESD data on disk (and one on tape at the production site) nReprocessed ESDs also get exchanged between paired Tier-1s of similar capacity  BNL  IN2P3CC+FZK, NIKHEF/SARA  ASGC+TRIUMF+RAL, CNAF  RAL, PIC  NDGF l The Tier-2s receive from “their” Tier-1 a fraction of AOD (and smaller fractions of ESD and RAW) compatible with their DISK size nTier-2s in European countries with a Tier-1 get globally a full set of AOD nSome “large” Tier-2s also get a full set of AOD l CPU capacity at Tier-2s is split between analysis (proportional to the data they hold on disk) and simulation nSimulation output is transferred to Tier-1s that have storage capacity

9. ATLAS Computing Requirements LHCC - 19 March 2007 9 Reality check l We always compare our requirements with the pledges in the RRB tables l For 2007-2008, the sum of the pledges approximately matches our requirements nLater on there may be a problem, especially with storage space l The pledges for 2007 were supposed to be made available on 1st July nBut many computing centres have capacities several factors lower right now, and not enough purchasing actions in the pipeline nAbout 1/2 of the 2007 capacity should have been available in 2006, but his did not happen l The result is that we have full disks in most Tier-1s and had to reduce the production rates l We need that people take MoU pledges as the basis of their investment plans, as we rely on these pledges for our own planning

10. ATLAS Computing Requirements LHCC - 19 March 2007 10 Summary 2007 timeline l Running continuously throughout the year (increasing rates): nSimulation production nCosmic ray data-taking (detector commissioning) l January to June: nData streaming tests l March through May: nIntensive Tier-0 tests l From February onwards: nData Distribution tests l From March onwards: nDistributed Analysis (intensive tests) l May to July: nCalibration Data Challenge l June to October: nFull Dress Rehearsal l November: nGO!