Large scale data flow in local and GRID environment V.Kolosov, I.Korolko, S.Makarychev ITEP Moscow

Research objectives Plans: Large scale data flow simulation in local and GRID environment. Done: 1.Data flow optimization in realistic DC environment ALICE and LHCb MC production 2.Simulation of intensive data flow during data analysis (CMS-like jobs)

main components ITEP LHC computer farm (1) 64  Pentium IV PC modules ( ) A. Selivanov (ITEP-ALICE) a head of the ITEP-LHC farm

BATCH nodes ITEP LHC computer farm (2) CPU:64 PIV-2.4GHz (hyperthreading) RAM:1 GB Disks:80 GB Mass storage 18 TB disk space on Gbit/s network 100 Mbit/s CERN ~622 Mbit/s 32 (LCG) + 32 (PBS)

ITEP LHC FARM since LHC experiments are using ITEP facilities permanently till now we were mainly producing MC samples ITEP view from GOC Accounting Services

ALICE and LHCb DC (2004) ALICE Determine readiness of the off-line framework for data processing Validate the distributed computing model 10% test of the final capacity physics: hard probes (jets, heavy flavours) & pp physics LHCb Studies of high level triggers S/B studies, consolidate background estimates, background properties Robustness test of the LHCb software and production system Test of the LHCb distributed computing model Massive MC production ( ) M events in 3 months

ALICE and LHCb DC (2004) 1 job – 1 event Raw event size: 2 GB ESD size: MB CPU time: 5-20 hours RAM usage: huge Store local copies Backup sent to CERN ALICE - AliEn Massive data exchange with local disk servers 1 job – 500 events Raw event size: ~1.3 MB DST size: MB CPU time: hours RAM usage: moderate Store local copies of DSTs DSTs and LOGs sent to CERN LHCb - DIRAC Often communication with central services

Optimization April – start massive LHCb DC 1 job/CPU – everything OK use hyperthreading - 2jobs/CPU - increase efficiency by 30-40% May – start massive ALICE DC bad interference with LHCb jobs often crashes of NFS restrict ALICE queue to 10 simultaneous jobs, optimize communication with disk server June – Septembersmooth running share resources, LHCb - June July,ALICE – August September careful online monitoring of jobs (on top of usual monitoring from collaboration)

Monitoring Often power cuts in summer (4-5 times)-5% all intermediate steps are lost (…) provide reserve power line and more powerful UPS Stalled jobs-10% infinite loops in GEANT4 (LHCb) crashes of central services write simple check script and kill such jobs (bug report is not sent…) Slow data transfer to CERN poor and restricted link to CERN problems with CASTOR automatic retry

DC Summary Quite visible participation in ALICE and LHCb DCs ALICE → ~5% contribution (ITEP part ~70%) LHCb → ~5% contribution (ITEP part ~70%) With only 44 CPUs Problems reported to colleagues in collaborations Today MC production is a routine task running on LCG (LCG efficiency is still rather low)

Data Analysis Distributed analysis – very different pattern of work load event size: 300 kB CPU time: 0.25 kSI2k/event CMS event size: 75 kB CPU time: 0.3 kSI2k/event LHCb Modern CPUs are ~1 kSI2k  4 events/sec. In 2 years from now 2-3 kSI2k  8-12 events/sec. Data reading rate ~ 3MB/sec Many (up to 100) jobs running in parallel Should we expect serious degradation of cluster performance during simultaneous data analysis by all LHC experiments ?

Simulation of data analysis CMS-like job analyses 1000 events in 100 seconds DST files are stored on a single file server Smoothly increase number of parallel jobs, measuring DST reading time increase number of allowed nfs daemons (8 – default value)

Simulation of data analysis simultaneous jobs getting data from single file server are running without significant degradation of performance Further increase of jobs number is dangerous Full load of cluster with analysis jobs decreases the efficiency of CPU usage by a factor of 2 (32 CPUs only…) file server load

Summary To analyze LHC data (in 2 years from now) we have to improve our clusters considerably: use faster disks for data storage (currently 70 MB/s) use 10 Gbit network for file servers distribute data over many file servers optimize structure of cluster