Simulation use cases for T2 in ALICE Latchezar Betev T2 Workshop CERN – June 12, 2006

ALICE T2 simulation use cases Outline The ALICE computing models and tiered structure MC production – specifics T2 setup – internal structure and data transfers Testing of MC production ALICE T2 simulation use cases

The ALICE computing model Minimum of intrinsic hierarchy and specific resources categories: Intelligent workload scheduling allowing for an optimal resources utilization With the exception of critical tasks, the tiered computing centres architecture is not strictly enforced in ALICE The difference between T1 and T2 is: Absence of a MSS in a T2 – custodial storage is ’remote’ from a T2 point of view Lower QoS – typically service 24/7 is not requested by the MoU, however the T2s are typically showing excellent support ALICE T2 simulation use cases

The ALICE computing model (2) Distribution of tasks per tiers in the ALICE computing model T2s are responsible for MC simulation and chaotic data analysis ALICE T2 simulation use cases

ALICE T2 simulation use cases MC production on T2s There is approximately as many MC events in ALICE as data events Thus the role of the T2s is rather important The amount of computing resources (CPU, disk storage) provided by T2s is > 50% of the total We have currently ~35 T2 sites providing 2000KSi2K CPU units and ~350 TB of disk space In 2007-2008, the number of sites is going to be about the same, however the CPU and storage is going to grow x2 Production of MC events MC production job is like any other job in the ALICE model All jobs (including MC production) are submitted to the central ALICE GRID task queue – no backdoor access to resources This allows to prioritize the submission to the sites Since the MC production does not require a large amount of input data, the matchmaking between the jobs and the site resources is trivial ALICE T2 simulation use cases

ALICE T2 simulation use cases MC production on T2s (2) Typical jdl of a MC job in ALICE ALICE T2 simulation use cases

ALICE T2 simulation use cases MC production on T2s (3) The application software is distributed though the AliEn tools (PackMan) For ‘official’ production User production PackMan also tracks the software versions and dependencies The application software includes Event genarators (HIJING, PYTHIA,…) Transport code (GEANT3, FLUKA) Reconstruction code (AliRoot) MC events are stored on the local SE and transferred to the hosting T1 for custodial storage Analysis of these events (at the T2) from all members of the collaboration is assured through the GRID access ALICE T2 simulation use cases

ALICE T2 simulation use cases MC production on T2s This model of production has been (and is) extensively tested in 3 data challenges: PDC’04, PDC’05 and the ongoing PDC’06 Standard setup – LCG/gLite with an ALICE VO-box (as on the T1s) We do require a VO-box at every site supporting ALICE ALICE-specific services and their function is well-documented All job submission to T2s is through the GRID Specific requirements for the T2s (MC induced, but usable also for other tasks) Large amount of memory consumption per job: 2GB max => 2GB RAM per CPU(core) Job duration – typically 8 KSI2k hours (generation, transport, reconstruction) Input data – small set of configuration files + conditions Output data – up to 1.5GB/job, standard 300 MB, this amount of scratch disk space is required on the WN The jobs are (naturally) CPU-intensive, no stringent requirement on storage One ALICE specific queue at the site – all prioritization is handled in the central AliEn task queue prior to job submission Produced MC data are stored on the local SE and transferred for custodial storage to the host T1 ALICE T2 simulation use cases

ALICE T2 simulation use cases T2 support Regional principle – T1 expert is responsible for the country/region T2s Setup of ALICE specific services Training of T2 personnel Site specific problem tracking and solving – through direct contact with administrators and through GGUS ticketing system The latter is getting better with time ALICE T2 simulation use cases

PDC’06 specific tests of T2s Generally, ALICE is currently doing tests of all elements of the computing model MC production – ongoing on all configured sites Local storage of data – on xrootd enabled disk servers (see presentation of A.Trunov at this workshop) In August 2007 – T2->T1 transfer (FTS) tests: Relational matrix T2-> host T1 is being build Installation of FTS client infrastructure User analysis on T2s is going to be discussed in another presentation (see talk of A. Peters tomorrow) ALICE T2 simulation use cases

ALICE T2 simulation use cases Conclusions T2s will be responsible for MC production and chaotic user analysis They are integrated in ALICE through the GRID tools for job submission/storage and data migration In the role of MC producers, the T2s have been extensively used in a series of data challenges Few remaining tools for data replication to be tested and integrated this year The MC production is equivalent (as is treated) as the other computational tasks (data production, analysis) in the ALICE model and as such does not induce any special requirements ALICE T2 simulation use cases