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ALICE Data Challenges. Fons Rademakers. Data Challenge. When fully operational ALICE will take data with a rate of 1.5 GB/s An order of magnitude higher than any of the other LHC experiments Since we are unique we can not piggyback on ATLAS/CMS/IT R&D. Objectives.

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alice data challenges
ALICE Data Challenges

Fons Rademakers

data challenge
Data Challenge
  • When fully operational ALICE will take data with a rate of 1.5 GB/s
  • An order of magnitude higher than any of the other LHC experiments
  • Since we are unique we can not piggyback on ATLAS/CMS/IT R&D
objectives
Objectives
  • Simulate the ALICE on-line and off-line data recording and processing chain
  • Track technologies:
    • DATE, ROOT, MSS, networking, CPU\'s and OS\'es
  • Repeat frequently to collect data points to see if we will be ready for 1.5 GB/s in 2005

Be ready for T=0 with as little surprises as possible

first data challenge
First Data Challenge
  • To store 10TB of raw data in a ROOT DB on HPSS within 5 days (i.e. 25 MB/s)
  • To test the following technologies:
    • DATE, ROOT, HPSS, GB ethernet, Linux and PC\'s
  • Very simple event model, but fairly realistic raw, tag and catalogue database environment
  • Executed in March 1999
adc1 data flow
ADC1 Data Flow

Computer center

NA57 Data source

Intel/Linux PC

PowerPC/AIX

ROOT

objectifier

LDC

pipe

GDC

Event Builder

5 MB/s

switch

GB eth

rfcp

LDC

5 MB/s

disk

GB eth

DATE = LDC+GDC

5 MB/s

HPSS

RS6000/AIX

5 node cluster

date data source
DATE Data Source
  • DATE is developed by the ALICE DAQ team and used by NA57 and COMPASS
    • See talk by R. Divia (B293) this afternoon
  • LDC = Local Data Concentrator
  • GDC = Global Data Collector
  • In this setup the LDC\'s generated bit patterns simulating (NA57) events (size 400 - 500 KBytes/event)
raw data db
RAW Data DB
  • Raw data DB contains AliEvent objects, which contain:
    • an AliEventHeader object
      • 16 data members (72 bytes)
    • an AliRawData object
      • char array (variable length, 400-500 kB)
  • AliEvent objects are stored in a single TTree container with two branches (for the two contained objects)
raw data db cont
RAW Data DB (cont.)
  • No compression (need more CPU power)
  • Size of individual raw DB\'s typically between 250 MB and 1.5 GB (tunable parameter)
  • As soon as a raw DB is closed it is moved to HPSS via rfcp (part of CERN SHIFT software interfaced to HPSS)
tag db
Tag DB
  • Tag DB contains AliEventHeader objects, which contain:
    • size, type, run number, event number, burst number, trigger, time, detector id, etc.
  • AliEventHeader objects are stored in a single TTree with 16 branches (one for each header data member)
  • Compressed
  • Stays on disk
  • Used for fast event selection
run catalog db
Run Catalog DB
  • Run DB contains one AliStats object per produced raw data DB
  • An AliStats object contains:
    • filename of raw DB, number of events, begin/end run number, begin/end event number, begin/end time, file size of raw DB, compression factor, quality histogram (TH1F)
  • Compressed
  • Stays on disk
  • Used for matching run/event with raw DB
slide15

NA57 Data source

Computer center

9 PowerPC/AIX

LDC

Intel/Linux PC Cluster

5 MB/s

LDC

Switch

Event

Filter

5 MB/s

GDC

Event Builder

GB eth

ROOT

objectifier

Switch

Pipe

5 IntelPC/Linux

10 MB/s

LDC

Switch

GB eth

10 MB/s

LDC

10 MB/s

Catalog

Tag DB

HPSS/

CASTOR

MSS

Alice DAQ Lab Data source

DATE = LDC+GDC

20 node cluster

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