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LHCb on the Grid A Tale of many Migrations

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Presentation on theme: "LHCb on the Grid A Tale of many Migrations"— Presentation transcript:

1 LHCb on the Grid A Tale of many Migrations
Raja Nandakumar

2 LHCb computing model CERN (Tier-0) is the hub of all activity
Full copy at CERN of all raw data and dst-s All T1s have a full copy of dst-s Simulation at all possible sites (CERN, T1, T2) LHCb has used about 120 sites on 5 continents so far Reconstruction, Stripping and Analysis at T0 / T1 sites only Some analysis may be possible at “large” T2 sites in the future Almost all the computing (except for development / tests) will be run on the grid. Large productions : production team Ganga (Dirac) grid user interface

3 LHCb storage on Tier-1 LHCb storage primarily on the Tier-1s and CERN
RAL dCache scheduled to stop in May 2008 Scale of storage usage in Oct 2007 Disk : ~75 TB Tape : ~45 TB 104 tapes in total Required storage on CASTOR provided on demand by Tier-1 CASTOR stable by Sept 2007 v2.1.4 (in Sept 2007) Great work done by Tier-1 in getting CASTOR operational A few delays from LHCb side in working on migration CHEP ‘07, DIRAC3 development issues, etc. LHCb data migration began in Nov 2007

4 LHCb disk migration Disk migration began ~ 20 Nov 2007
Completed ~ 20 Dec 2007 A few minor issues / configuration problems. Quickly solved. All disk servers finally released in Feb 2008 Files with transfer errors were re-transferred. Files transferred using FTS between dCache and CASTOR DIRAC interface for LHCb, to automatically register files after transferring Bulk LFC cleanup after groups of files are transferred Peak rates of about 100 MB/s from dCache to CASTOR Also depended on number of different servers on each end Mostly smooth operations Problems : minor, human LHCb running off CASTOR since mid Jan 2008 A few worries, but mostly fine Disk

5 LHCb tape migration Tape migration first tried ~ 7 Dec 2007
In full scale in Jan 2008 Many iterations to get current procedure Tape staging by hand FTS does not automatically stage files on tape Automatic staging of files not practical Problems with coordination of tape staging (RAL) and FTS job submission (CERN) Files getting wiped off dCache before transfer Now staging two tapes at a time Wait for FTS jobs to complete before staging next tapes ~ 50 tapes to go still … Fine when it is running ~ 60 MB/s transfer rates ~ 4 hours to stage a tape ~ 2 hours to transfer it to CASTOR ~ 2 tapes a day Tape

6 LHCb storage on Tier-1 LHCb running off CASTOR now
Ignore data only in dCache tape Transfers into CASTOR running fine Currently use srm-v1 for official production srm-v2 used in CCRC08 Critical service for LHCb File replication using gLite FTS TURLs retrieved via gfal for access via available site protocols root, rfio, dcap, gsidcap RDST output file upload to local Tier-1 SE via lcg-utils / gfal File removal using gfal Tier-0,1 Storage Elements providing SRM2 spaces: LHCb_RAW (T1D0), LHCb_RDST (T1D0) LHCb_M-DST (T1D1), LHCb_DST (T0D1) LHCb_FAILOVER (T0D1) Used for temporary upload in case of destination unavailability Testing of srm-v2 is a key part of CCRC’08 for LHCb To be used for all production jobs As soon as DIRAC3 is in full production mode

7 LHCb on RAL-CASTOR A few issues running off CASTOR
Hang when too many jobs run off data on a single server A single server can currently support ~ 200 lsf job slots A single job can have 1-3 files open on the server Can easily have 200 jobs running Currently kill all the file requests to restore the server Bonny / Shaun / Chris Need for more CASTOR monitoring tools Will be good to have rootd / xrootd also Pausing of jobs during downtime (works at CERN) Jobs should pick up from where they were, when they are restarted A few non-castor problems too Backplanes replacement / fire hazard Power down due to transformer shutdown RAL first to publish CASTOR storage to the IS Very very useful Overall service - stable

8 LHCb on the Grid DIRAC is LHCb’s interface to the grid DIRAC3
Written mostly in python Pilot agent paradigm Fine grained visibility of grid to the jobs and DIRAC3 servers DIRAC3 Re-writing of DIRAC using 4 years of experience Main ideas / framework retained Many changes in algorithms and implementations Security : Authentication & logging for all operations Separate out generic and LHCb-specific modules Better designed to support more options srm v2, gLite WMS, generic pilots, … Job throttling, job prioritisation, generic pilots, … DIRAC2 DIRAC3

9 DIRAC LFC checkData Job Receiver JDL Job Receiver Data Optimizer Task
Queue Sandbox Job Input JobDB Job JDL Agent Director checkJob getReplicas Agent Monitor checkPilot Matcher CE JDL WMS Admin getProxy Job Monitor RB RB / WMS Pilot Job SE uploadData DIRAC services LCG Workload On WN getSandbox CE VO-box putRequest Job Wrapper execute (glexec) Pilot Agent WN User Application fork

10 LHCb and DIRAC3 DIRAC3 status –
Still under development Major parts already running Used in CCRC08 So far, successful testing of simulation and reconstruction workflows User analysis to be integrated with DIRAC3 once it is stable in production Bookkeeping in DIRAC3 Bookkeeping not to be stand alone Will be a set of fully integrated services New : effort from Ireland in the web / user interface of bookkeeping Critical for Monte Carlo analysis and in future to data analysis

11 DIRAC3 monitoring Note the authentication at top right
Not needed for browsing the jobs Needed to perform actions

12 LHCb and CCRC08 Planned tasks : Test the LHCb computing model
Raw data distribution from pit to T0 centre Use of rfcp into CASTOR from pit - T1D0 Raw data distribution from T0 to T1 centres Use of FTS - T1D0 Recons of raw data at CERN & T1 centres Production of rDST data - T1D0 Use of SRM 2.2 Stripping of data at CERN & T1 centres Input data: RAW & rDST - T1D0 Output data: DST - T1D1 Use SRM 2.2 Distribution of DST data to all other centres Use of FTS - T0D1 (except CERN T1D1) First three tasks successfully accomplished Tests of stripping workflow within DIRAC3 ongoing

13 Data distribution Site CPU Share (Percentage) RAW Share (Percentage)
CERN 14 100 GridKa 11 12 IN2P3 25 29 CNAF 9 NIKHEF 26 30 PIC 4 5 RAL 13

14 RAW data transfers Data transfers mimicked LHC data taking
6 hours on, 6 hours off A few pauses for software upgrades Peak of 125 MB/s (Feb 12th) Nominal rate : 70 MB/s Some Tier-1 problems seen 0 checksum mismatches No problems seen at RAL ! S. Paterson – CCRC F2F meeting Tier-1 transfers

15 FTS performance Histograms of time between a file being Assigned andTransferred to the LHCb Tier-1s (minutes) FTS submit / monitor / done cycle Most sites show stable behaviour S. Paterson – CCRC F2F meeting

16 CCRC’08 LHCb issues Automatic job submission successfully demonstrated
Problems setting up job workflows Had planned to run 23K jobs over 2 weeks Cpu time underestimated for reconstruction Many jobs overshot wall time and were killed Systematic over all Tier-1s DIRAC3 servers downtime Lost connection to running jobs Not possible to recover many jobs Configuration service unstable Needed to be restarted regularly Need for backup / failover systems

17 CCRC’08 site issues Problems on dCache sites CERN – CNAF –
Configuration of timeouts on gsidcap ports dCache not releasing space reserved even if files are deleted. Data transfer, access problems due to load on pnfs server (IN2P3) Problem with solaris servers at SARA CERN – AFS instabilities CNAF – Low CASTOR lsf slots per server RAL : No problems S. Paterson – CCRC F2F meeting

18 Upcoming schedule March April May Later Introduce stripping workflow
Consider usage of xrootd protocol Helps with flickering data access April Migration of GridPP2+ to GridPP3 May 4 weeks of running at nominal rate If possible, include analysis Possibly using generic pilots Pending approval and deployment of glexec Ganga (migrating to v5!) for analysis job submission Later Data taking …

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