1. An introduction to the ATLAS Computing Model Alessandro De Salvo
Outline
The ATLAS Tier and Cloud model
The Tier centers
Data types
Data avilability in the Tiers
A. De Salvo – 20 Apr 2008

2. The ATLAS Tier and Cloud Model
Multi-Tier gerarchical model
Cloud model
Each Tier 1 center defines a Cloud
3 or 4 Tier2 centers are associated to each Cloud (Tier1), often on the basis of a geographical criteria

3. The ATLAS Tier1 centers ASGC (Taiwan) BNL (USA) CNAF (Italy)
AU-ATLAS, TW-FTT,AU-UNIMELB
BNL (USA)
AGLT2, BU, MWT2, OU, SLAC, UTA, WISC
CNAF (Italy)
LNF, MILANO, NAPOLI, ROMA1
FZK (Germany)
CSCS,CYF,DESY-HH,DESY-ZN,FZU,LRZ, FREIBURG, WUP
NDGF (Nordic Countries)
LYON (France)
BEIJING, CPPM, LAL, LAPP, LPC, LPNHE, NIPNE_02,NIPNE_07, SACLAY,TOKYO
PIC (Spain)
IFAE, IFIC, UAM,LIP
RAL (UK)
GLASGOW, LANCS, MANC, QMUL, DUR, EDINBURGH, OXF,CAM,LIV,BRUN,RHUL
SARA (Netherlands)
IHEP, ITEP, JINR, PNPI, SINP
TRIUMF (Canada)
ALBERTA, MONTREAL, SFU, TORONTO,UVIC

4. Tasks of the Tier centers
Raw data archival
Data distribution to the Tier1 centers
Prompt Reconstruction of the raw data within 48 hours
1st pass calibration within 24 hours
Distribution of the reconstruction output to the Tier1 centers
ESD, AOD and TAG
Tier-1
Long-term access and storage of a subset of the raw data
Backup copy of part of the raw data of another Tier1
Reprocessing of the raw data stored in each Tier1 with the final calibration and alignment parameters, after 2 months of the data taking
AOD distribution to the Tier2 centers
Archival of the MC data produced in the Tier2 centers
Group analysis
Centralized analysis of the physics groups
Tier-2
Monte Carlo simulation
User analysis
Off-site detector calibration (selected Tier2s only)

5. Data types and sizes Raw data ESD (Event Summary Data)
Byte-stream data coming from the trigger
ESD (Event Summary Data)
Output of the reconstruction
Tracks
Hits
Calorimeter clusters
Combined reconstruction objects …
Used for calibration, alignment, refitting
Generally used when the data in the AOD is not sufficient to complete the analysis
AOD (analysis Object Data)
Reduced format created for the analysis
Reconstructed physical quantities
Electrons, muons, taus, …
DPD (Derived Physics Data)
Reduced data for explicit usage in ROOT
1.6 MB
Target
500 kB
Currently
750/900 kB
Target
100 kB
Currently
250/290 kB
10% of AOD

6. Event size

7. Data distribution

8. Tier-0 throughput schema
TDAQ output rate = 320 MB/s ⇒ 200 Hz (trigger rate) · 1,6 MB (event size)
Dedicated optical-fiber connection Tier0 ↔ 10 Gbps

9. The Tier-0 center
The full set of RAW data and the primary ESD and AOD are stored at Tier-0

10. The Tier-1 centers

11. Tier-1 data and computing activities
A full copy of the RAW data in the Tier-1 centers (10% on disk)
Double-copy of the ESD dta in the Tier-1 centers
A full copy of AOD and TAG in each Tier-1
Each Tier-1 reprocesses its own RAW data and replicates them
A full copy of physics group DPD per Tier-1
Computing activities (2008)
25% reprocessing
25% simulation
50% group analysis

12. The Tier-2 centers

13. Tier-2 data and computing activities
A full copy of the AOD and TAG data in each Tier-2 cloud
Physiscs group DPD and user DPD
RAW data in all the Tier-2 centers
30% in 2008
10% in 2009
ESD data in all the Tier-2 centers
50% in 2008
30% in 2009
Computing activities (2008)
15% reconstruction
37% simulation
48% user analysis