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

2. 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

3. 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

4. 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

5. 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 , 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

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

7. 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

8. 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

9. 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

10. 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

11. 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