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CRAB: a tool for CMS distributed analysis in grid environment

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Federica Fanzago INFN PADOVA. CRAB: a tool for CMS distributed analysis in grid environment. Introduction. CMS “Compact Muon Solenoid” is one of the four particle physics experiment that will collect data at LHC “Large Hadron Collider” starting in 2007 at CERN

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CMS “Compact Muon Solenoid” is one of the four particle physics experiment that will collect data at LHC “Large Hadron Collider” starting in 2007 at CERN

CMS will produce a large amount of data (events) that should be made available for analysis to world-wide distributed physicists

  • CMS will produce
    • ~2 PB events/year (assumes startup luminosity 2x1033 cm-2 s-1)
  • All events will be stored into files
    • O(10^6) files/year
  • Files will be grouped in Fileblocks
    • O(10^3) Fileblocks/year
  • Fileblocks will be grouped in Datasets
    • O(10^3) Datasets (total after 10 years of CMS)
    • 0.1- 100 TB

“bunch crossing” every 25 nsecs.

100 “triggers” per second

Each triggered event ~1 MB in size

issues and help
How to manage and where to store this huge quantity of data?

How to assure data access to physicists of CMS collaboration?

How to have enough computing power for processing and data analysis?

How to ensure resources and data availability?

How to define local and global policy about data access and resources?

 CMS will use a distributed architecture based on grid infrastructure

Tools for accessing distributed data and resources are provided by WLCG (World LHC Computing Grid) with two main different flavours

LCG/gLite in Europe, OSG in the US

Issues and help
cms computing model
CMS computing model

Offline farm

recorded data

Online system

CERN Computer center

Tier 0

. .


Regional Center


Regional Center


Regional Center

Tier 1

. . .

Tier 2

Tier2 Center

Tier2 Center

Tier2 Center


Tier 3



The CMS offline computing system is arranged in four Tiers and is geographically distributed

Remote data


via grid

analysis what happens in a local environment
Analysis:what happens in a local environment...

User writes his own analysis code and configuration parameter card

Starting from CMS specific analysis software

Builds executable and libraries

He apply the code to a given amount of events, whose location is known, splitting the load over many jobs

But generally he is allowed to access only local data

He writes wrapper scripts and uses a local batch system to exploit all the computing power

Comfortable until data you’re looking for are sitting just by your side

Then he submits all by hand and checks the status and overall progress

Finally collects all output files and store them somewhere

and in a distributed grid environment
...and in a distributed grid environment

The distributed analysis is a more complex computing task because it assume to know:

which data are available

where data are stored and how to access them

which resources are available and are able to comply with analysis requirements

grid and CMS infrastructure details

But users don\'t want deal with these kind of problem

Users want to analyze data in “a simple way” as in local environment

distribution analysis chain
Distribution analysis chain...

To allow analysis in distributed environment, the CMS collaboration is developing some tools interfaced with grid services, that include

Installation of CMS software via grid on remote resources

Data transfer service: to move and manage a large flow of data among tiers

Data validation system: to ensure data consistency

Data location system: to keep track of data available in each site and to allow data discovery, composed by

Central database (RefDB) that knows what kind of data (dataset) have been produced in each Tier

Local database (PubDB) in each Tier, with info about where data are stored and their access protocol

CRAB: Cms Remote Analysis Builder...

and crab role
... and CRAB role

CRAB is a user-friendly tool whose aim is to simplify the work of users with no knowledge of grid infrastructure to create, submit and manage job analysis into grid environments.

written in python and installed on UI (grid user access point)

Users have to develop their analysis code in a interactive environment and decide which data to analyse.

They have to provide to CRAB:

Dataset name, number of events

Analysis code and parameter card

Output files and handling policy

CRAB handles data discovery, resources availability, job creation and submission, status monitoring and output retrieval

how crab works
How CRAB works

Job creation: crab –create N (or all)

data discovery: sites storing data are found querying RefDB and local PubDBs

packaging of user code: creation of a tgz archive with user code (bin, lib and data)

wrapper script (sh) for the real user executable

JDL file, script which drives the real job towards the “grid”

splitting: according to user request (number of events per job and in total)

Job submission: crab –submit N (or all) -c

jobs are submitted to the Resource Broker using BOSS, the submitter and tracking tool interfaced with CRAB

jobs are sent to those sites which host data

how crab works 2
How CRAB works (2)

Job monitoring: crab –status (n_of_job)

the status of all submitted jobs is checked using Boss

Job output management: crab –getoutput (n_of_job)

following user request CRAB can

copy them back to the UI ...

... or copy to a Storage Element

Job resubmission: crab –resubmit n_of_job

if job suffers grid failure (aborted or cancelled status)

crab experience
CRAB experience

Used by tens of users to access remote MC data for Physics TDR analysis

~7000 Datasets available for O(10^8) total events, full MC production

CMS users, via CRAB, use two dedicated Resources Brokers (at CERN and at CNAF) knowing all CMS sites

CRAB proves that CMS users are able to use available grid services and that the full analysis chain works in a distributed environment!

crab usage

Top 20 CE where

CRAB-Jobs run

Top 20 dataset/owner

requested from users

CRAB usage

CRAB is currently used to analyse

data for the CMS Physics TDR

(being written now…)

The total number of jobs submitted to the grid using CRAB during the second half of the last year is more than 300’000 by 40-50 users.

crab future
CRAB future
  • As CMS analysis framework and grid middleware evolve:
    • CRAB has to adapt to cope with these changes and always guarantee its usability and thus remote data access to users
      • New data discovery components (DBS, DLS) that will substitute RefDB and PubDB
      • New Event Data Model (as analysis framework)
      • gLite, new middleware for grid computing
  • Open issues to be resolved (number of users and submitted jobs is increasing…)
    • Jobs policies and priorities at VO level: for example
      • for next tree weeks Higgs group users have priorities over other groups
      • tracker alignment jobs performed by user xxx must start immediately
    • Bulk submission: handle 1000 jobs as a single task, just one submission/status/...
crab future 2
CRAB future (2)
  • CRAB will be split in two different components to minimize the user effort to manage analysis jobs and obtain their results.
  • Some user actions will be delegated to “not user dependent” services, that take care to follow job evolution on the grid, get results and return them to user
  • The Me/MyFriend idea:
    • Me: the user desktop (laptop or shell), where working environment is and where user can work interactively. For user operation as:
      • job creation
      • job submission
    • MyFriend: a set of robust services running 24x7 to guarantee the execution of:
      • job tracking
      • resubmission
      • output retrieval

CRAB was born in April ’05

A big effort has been done to understand user needs and how to use in the best way services provided by grid

Lot of work have been made to make it robust, flexible and reliable

Users appreciate the tool and are asking for further improvements

CRAB has been used by many CMS collaborators to analyze remote data for CMS Physics TDR, otherwise not accessible

CRAB is used to continuously test CMS Tiers to prove the whole infrastructure robustness

The use of CRAB proves the complete computing chain for distributed analysis works for a generic CMS user !


back up

Back-up slide

statistics with crab 1
Statistics with CRAB(1)

# of jobs

From 10-07-05 to 22.01.06

The weekly rate of the

CRAB-jobs flow is:




(%) jobs


statistics with crab 2


% of jobs which arrive

to WN (remote CE) and run

Statistics with CRAB(2)


All CE