1. A tool to enable CMS Distributed Analysis
CRAB
A tool to enable CMS Distributed Analysis

2. CMS (fast) overview CMS will produce a large amount of data (events)
~2 PB/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)

3. CMS Computing Model . . . . . Tier 0 Tier 1 Tier 2 Tier 3 Offline farm
Online system
Tier 0
Tier 1
Tier 2
Tier 3
Offline farm
CERN Computer center
. .
Tier2 Center
InstituteB
InstituteA
. . .
workstation
Italy
Regional Center
Fermilab
France
recorded data
The CMS offline computing system is arranged in four Tiers and is geographically distributed

4. So what? Large amount of data to be analyzed
Large community of physicists which wants to access data
Many distributed sites where data will be stored

5. Help!
WLCG, WorldWide LHC Computing Grid, that is a distributed computing environment
Two main different flavours
LCG/gLite in Europe, OSG in the US
CRAB a python tool which helps the user to build, manage and control analysis jobs over grid environments

6. Typical user analysis workflow
User writes his/her own analysis code
Starting from CMS specific analysis software
Builds executable and libraries
He wants to apply the code to a given amount of events splitting the load over many jobs
But generally he is allowed to access only local data
He should write wrapper scripts and use a local batch system to exploit all the computing power
Comfortable until data you’re looking for are sitting just by your side
Then should submit all by hand and check the status and overall progress
Finally should collect all output files and store them somewhere

7. CRAB main purposes
Keeps easy to create large number of user analysis job
Assume all jobs are the same except for some parameters (event number to be accessed, output file name…)
Allows to access distributed data efficiently
Hiding WLCG middleware complications. All interactions are transparent for the end user
Manages job submission, tracking, monitoring and output harvesting
User doesn’t have to take care about how to interact with sometimes complicated grid commands
Leaves time to get a coffee …

8. Log Files/(Job output)
CRAB workflow
1) Data location UI
RefDb (DBS) DB
CRAB
2) Job preparation
3) Job submission
PubDb (DLS)
4) Job status DB
5) Job output retrieval RB
LCG/OSG
Local file catalog CE CE CE CE CE CE CE SE SE
Data WN WN WN WN WN WN WN WN WN WN WN WN WN WN WN WN
Job output
Log Files/(Job output)

9. Main CRAB functionalities
Data discovery
Data are distributed so we need to know where data have been sent
Job creation
Both .sh (wrapper script for the real executable) and .jdl (a script which drives the real job towards the “grid”)
User parameters passed via config file (executable name, output file names, specific executable parameters…)
Job submission
Scripts are ready to be sent to those sites which host data
Boss, the job submitter and tracking tool, takes care of submitting jobs to the Resource Broker

10. Main CRAB functionalities (cont’d)
CRAB monitors, via Boss, the status of the whole submission
The user has to ask for jobs status
When jobs finish CRAB retrieves all output
Both standard output/error and relevant files produced by the analysis code
Either the job copies the output on the SE
Or it takes it back to the UI

11. Most accessed dataset since last July
So far (so good?)
CRAB is currently used to analyze data for the CMS Physics TDR (being written now…)
Most accessed dataset since last July
D.Spiga: CRAB Usage and jobs-flow Monitoring (DDA-252)

12. Some statistics CRAB jobs so far Most accessed sites since July 05
D.Spiga: CRAB Usage and jobs-flow Monitoring (DDA-252)

13. Crab usage during CMS SC3
CRAB has been extensively used to test CMS T1 sites partecipating SC3
The goal was to stress the computing facilities through the full analysis chain over all distributed data
J. Andreeva: CMS/ARDA activity within the CMS distributed computing system (DDA-237)

14. Crab (and CMS comp) evolves
CRAB needs to evolve to integrate with new CMS computing components
New data discovery components (DBS, DLS):under testing
New Event Data Model
New computing paradigm
Integration into a set of services which manage jobs on behalf of the user allowing him to interact only with “light” clients

15. Conclusions CRAB was born in April ’05
Lot of work and efforts have been made to make it robust, flexible and reliable
Users appreciate the tool and are asking for further improvements
Crab has been used to analyze data for CMS Physics TDR
CRAB is used to continuously test CMS Tiers to prove the whole infrastructure robustness

16. Pointers CRAB web page CRAB monitoring ARDA monitoring for CRAB jobs
Links to documentation, tutorials and mailing lists
CRAB monitoring
ARDA monitoring for CRAB jobs