Presentation on theme: "The ATLAS Computing Model Roger Jones Lancaster University CHEP06 Mumbai 13 Feb. 2006."— Presentation transcript:
The ATLAS Computing Model Roger Jones Lancaster University CHEP06 Mumbai 13 Feb. 2006
RWL Jones 13 Feb. 2006 Mumbai 2 Overview Brief summary ATLAS Facilities and their rolesBrief summary ATLAS Facilities and their roles Growth of resourcesGrowth of resources CPU, Disk, Mass Storage Network requirementsNetwork requirements CERN Tier 1 Tier 2 Operational Issues and Hot TopicsOperational Issues and Hot Topics
RWL Jones 13 Feb. 2006 Mumbai 3 Computing Resources Computing Model fairly well evolved, documented in C-TDRComputing Model fairly well evolved, documented in C-TDR Externally reviewed http://doc.cern.ch//archive/electronic/cern/preprints/lhcc/public/lh cc-2005-022.pdfhttp://doc.cern.ch//archive/electronic/cern/preprints/lhcc/public/lh cc-2005-022.pdf There are (and will remain for some time) many unknownsThere are (and will remain for some time) many unknowns Calibration and alignment strategy is still evolving Physics data access patterns MAY be exercised from June Unlikely to know the real patterns until 2007/2008! Still uncertainties on the event sizes, reconstruction time Lesson from the previous round of experiments at CERN (LEP, 1989-2000)Lesson from the previous round of experiments at CERN (LEP, 1989-2000) Reviews in 1988 underestimated the computing requirements by an order of magnitude!
RWL Jones 13 Feb. 2006 Mumbai 4 ATLAS Facilities Event Filter Farm at CERNEvent Filter Farm at CERN Located near the Experiment, assembles data into a stream to the Tier 0 Center Tier 0 Center at CERNTier 0 Center at CERN Raw data Mass storage at CERN and to Tier 1 centers Swift production of Event Summary Data (ESD) and Analysis Object Data (AOD) Ship ESD, AOD to Tier 1 centers Mass storage at CERN Tier 1 Centers distributed worldwide (10 centers)Tier 1 Centers distributed worldwide (10 centers) Re-reconstruction of raw data, producing new ESD, AOD Scheduled, group access to full ESD and AOD Tier 2 Centers distributed worldwide (approximately 30 centers)Tier 2 Centers distributed worldwide (approximately 30 centers) Monte Carlo Simulation, producing ESD, AOD, ESD, AOD Tier 1 centers On demand user physics analysis CERN Analysis FacilityCERN Analysis Facility Analysis Heightened access to ESD and RAW/calibration data on demand Tier 3 Centers distributed worldwideTier 3 Centers distributed worldwide Physics analysis
RWL Jones 13 Feb. 2006 Mumbai 5 Processing Tier-0:Tier-0: Prompt first pass processing on express/calibration physics stream 24-48 hours later, process full physics data stream with reasonable calibrations Implies large data movement from T0 T1s Tier-1:Tier-1: Reprocess 1-2 months after arrival with better calibrations Reprocess all resident RAW at year end with improved calibration and software Implies large data movement from T1T1 and T1 T2
RWL Jones 13 Feb. 2006 Mumbai 6 Analysis model Analysis model broken into two components Scheduled central production of augmented AOD, tuples & TAG collections from ESD Derived files moved to other T1s and to T2s Chaotic user analysis of augmented AOD streams, tuples, new selections etc and individual user simulation and CPU-bound tasks matching the official MC production Modest job traffic between T2s
RWL Jones 13 Feb. 2006 Mumbai 7 Inputs to the ATLAS Computing Model (1)
RWL Jones 13 Feb. 2006 Mumbai 8 Inputs to the ATLAS Computing Model (2)
RWL Jones 13 Feb. 2006 Mumbai 9 Tier 2 view Tier 0 view Data Flow EF farm T0EF farm T0 320 MB/s continuous T0 Raw data Mass Storage at CERNT0 Raw data Mass Storage at CERN T0 Raw data Tier 1 centersT0 Raw data Tier 1 centers T0 ESD, AOD, TAG Tier 1 centersT0 ESD, AOD, TAG Tier 1 centers 2 copies of ESD distributed worldwide T1 T2T1 T2 Some RAW/ESD, All AOD, All TAG Some group derived datasets T2 T1T2 T1 Simulated RAW, ESD, AOD, TAG T0 T2 Calibration processing?T0 T2 Calibration processing?
RWL Jones 13 Feb. 2006 Mumbai 11 Total ATLAS Requirements in for 2008
RWL Jones 13 Feb. 2006 Mumbai 12 Important points: Discussion on disk vs tape storage at Tier-1sDiscussion on disk vs tape storage at Tier-1s Tape in this discussion means low-access secure storage No disk buffers included except input to Tier 0 Storage of Simulation data from Tier 2sStorage of Simulation data from Tier 2s Assumed to be at T1s Need partnerships to plan networking Must have fail-over to other sites CommissioningCommissioning Requirement of flexibility in the early stages Simulation is a tunable parameter in T2 numbers!Simulation is a tunable parameter in T2 numbers! Heavy Ion running still under discussion.Heavy Ion running still under discussion.
RWL Jones 13 Feb. 2006 Mumbai 16 Required Network Bandwidth CaveatsCaveats No safety factors No headroom Just sustained average numbers Assumes no years/datasets are junked Physics analysis pattern still under study…
RWL Jones 13 Feb. 2006 Mumbai 17 T1 CERN Bandwidth I+O Mainly outward data movement The projected time profile of the nominal bandwidth required between CERN and the Tier-1 cloud.
RWL Jones 13 Feb. 2006 Mumbai 18 T1 T1 Bandwidth I+O About half is scheduled analysis The projected time profile of the nominal bandwidth required T1 and T1 cloud.
RWL Jones 13 Feb. 2006 Mumbai 19 T1 T2 Bandwidth I+O The projected time profile of the nominal aggregate bandwidth expected for an average ATLAS Tier- 1 and its three associated Tier-2s. Dominated by AOD
RWL Jones 13 Feb. 2006 Mumbai 20 Issues 1: T1 Reprocessing Reprocessing at Tier 1s is understood in principleReprocessing at Tier 1s is understood in principle In practice, requires efficient recall of data from archive and processing Pinning, pre-staging, DAGs all required? Requires the different storage roles to be well understood
RWL Jones 13 Feb. 2006 Mumbai 21 Issues 2: Streaming This is *not* a theological issueThis is *not* a theological issue All discussions are about optimisation of data access TDR has 4 streams from event filterTDR has 4 streams from event filter primary physics, calibration, express, problem events Calibration stream has split at least once since! At AOD, envisage ~10 streamsAt AOD, envisage ~10 streams ESD streaming?ESD streaming? Straw man streaming schemes (trigger based) being agreed Will explore the access improvements in large-scale exercises Will also look at overlaps, bookkeeping etc
RWL Jones 13 Feb. 2006 Mumbai 22 TAG Access TAG is a keyed list of variables/eventTAG is a keyed list of variables/event Two rolesTwo roles Direct access to event in file via pointer Data collection definition function Two formats, file and databaseTwo formats, file and database Now believe large queries require full databaseNow believe large queries require full database Restricts it to Tier1s and large Tier2s/CAF Ordinary Tier2s hold file-based TAG corresponding to locally-held datasets
RWL Jones 13 Feb. 2006 Mumbai 23 Conclusions Computing Model Data Flow understood for placing Raw, ESD and AOD at Tiered centersComputing Model Data Flow understood for placing Raw, ESD and AOD at Tiered centers Still need to understand data flow implications of Physics Analysis SC4/Computing System Commissioning in 2006 is vital.SC4/Computing System Commissioning in 2006 is vital. Some issues will only be resolved with real data in 2007-8Some issues will only be resolved with real data in 2007-8
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