1 / 25

ALICE computing Focus on STEP09 and analysis activities

ALICE computing Focus on STEP09 and analysis activities. Latchezar Betev Réunion LCG-France, LAPP Annecy May 19, 2009. Outline. General resources/T2s User analysis and storage on the Grid (LAF is covered by Laurent’s presentation) WMS Software distribution STEP 09

mwhite
Télécharger la présentation

ALICE computing Focus on STEP09 and analysis activities

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. ALICE computingFocus on STEP09 and analysis activities Latchezar Betev Réunion LCG-France, LAPP Annecy May 19, 2009

  2. Outline • General resources/T2s • User analysis and storage on the Grid (LAF is covered by Laurent’s presentation) • WMS • Software distribution • STEP 09 • Operations support

  3. French computing centres contribution for ALICE T1 – CCIN2P3 6 T2 + T2 federation (GRIF)

  4. Relative CPU share Last 2 months ~1/2 from T2s!

  5. Relative contribution – T2s • T2 share of the resources is substantial • (globally) T2s provide ~50% of the CPU capacity for ALICE, they should also provide ~50% of the disk capacity • The T0/T1 disk is mostly MSS buffer, therefore completely different function • T2 role in the ALICE computing model • MC production • User analysis • MC+RAW ESDs replicas are kept on T2 disk storage

  6. Focus on analysis • Grid responsiveness for user analysis • ALICE uses common Task Queue for all grid jobs, internal prioritization • Pilot Jobs are indispensible part of the schema • They check the ‘sanity’ of the WN environment (and die if something is wrong) • Pull the ‘top priority’ jobs for execution first

  7. Grid response time - user jobs Type 1 - jobs with little input data (MC) Average waiting time – 11 minutes Average running time – 65 minutes 62% probability of waiting time <5 minutes Type 2 – large input data ESDs/AODs (analysis) Average waiting time – 37 minutes Average running time – 50 minutes Response time proportional to number of replicas

  8. Grid response time – user jobs (2) • Type 1 (MC) can be regarded as ‘maximum Grid responce efficiency’ • Type 2 (ESDs/AODs) can be improved • Trivial - more data replication (not an option – not enough storage capacity) • Analysis train – grouping many analysis tasks in a common data set – improves the efficiency of tasks and resources utilization (CPU/Wall + storage load) • Non-local data access through xrootd global redirector • Inter-site SE cooperation, common file namespace • Off-site access to storage from a job – is that really ‘off limits’?

  9. Storage stability • Critical for the analysis – nothing helps if the storage is down • A site can have half of the WNs off, but not half of the storage servers… • Impossible to know before the client tries to access the data • Unless we allow the off-site access… • ALICE computing model foresees 3 active replicas of all ESDs/AODs

  10. Storage stability (2) • T2 storage stability test under load (user tasks + production)

  11. Storage availability scores • Storage type 1 – average 73.9% • Probability of all three alive (3 replicas) = 41% • This defines the job waiting time and success rate • xrootd native – average 92.8% • Probability of all three alive (3 replicas) = 87% • The above underlines the importance of extremely reliable storage, in the absence of infinite storage resources as compensation

  12. Storage continued • Storage availability/stability remains one of the top priorities for ALICE • For strategic directions see Fabrizio’s talk • All other parameters being equal (protocol access speed and security): ALICE recommends wherever feasible a pure xrootd installation • Ancillary benefit from site admin point of view – no databases to worry about + storage cooperation through global redirector

  13. Workload management: WMS and CREAM • WMS + gLite CE • Relatively long period of understanding the service parameters • Big effort by GRIF experts to provide a French WMS, now with high stability and reliability • Similar installations at other T1s (several at CERN) • Still ‘inherits’ the gLite CE limitations • CREAM CE • The future, gLite CE days are numbered • Strategic direction of the WLCG

  14. Workload management (2) • CREAM CE (cont’d) • ALICE requires a CREAM CE at every centre, to be deployed before start of data taking • Much better scalability, shown by extensive tests • Hands-off operation after initial (still time-consuming) installation • Excellent support by CNAF developers

  15. Software deployment • General need for improvement of software deployment tools • Software distribution is a ‘Class 1 service’ – shared software area WNs and VO-box • Always a (security related) point for critique • Heterogeneous queues: mixed 32- and 64-bit hosts, various Linux flavors, other system library differences, hence need for various application software versions • In addition, the shared area (typically NFS) • Is often overloaded • Single point of failure • One ‘bad installation’ is fatal for the entire site operation

  16. Packaging & size • Combine all the required grid packages into distributions • Full installation: 155 MB, mysql, ldap, perl, java... • VO-box: 122 MB, monitor, perl, interfaces, • User: 55 MB, API client, gsoap, xrootd • Worker node: 34 MB, min perl, openssl, xrootd • Experiment software: • AliRoot: 160 MB • ROOT: 60 MB • GEANT3: 25MB 300 MB to run jobs 16

  17. Use existing technology More than 150 million users!! http://bittorrent.com 17

  18. Torrent technology Download & seed alitorrent.cern.ch Download & seed Tracker Download & seed Site B No inter-site seeding Seeder Site A Download & seed Download & seed Download & seed

  19. Application software path • Torrent files created from the build system • One seeder at CERN • Standard tracker and seeder. • Get torrent client from ALICE web server • Aria2c • Download the files and install them • Seed the files while the job runs 19

  20. ALICE activities calendar – STEP’09 STEP’09 Cosmics data taking WMS and CREAM CE Reprocessing Pass 2 Analysis train Replication of RAW Data taking RAW deletion 12 01 02 03 04 05 06 07 08 09 10 11 12 2008 2009

  21. ALICE STEP’09 activities • Replication T0->T1 • Planned together with Cosmics data taking, must be moved forward, or • We can repeat the last year’s exercise, same rates (~100MB/sec), same destinations • Re-processing with data recalls from tape at T1 • Highly desirable exercise, the data is already at the T1 MSS • CCIN2P3 MSS/xrootd setup is being organized, we can export fresh RAW data into the buffer

  22. ALICE STEP’09 activities (2) • Non-Grid activity – transfer rate tests (up to 1.25GB/sec) DAQ@P2 to CASTOR • Validation of new CASTOR and xrootd transfer protocol for RAW • Will go on just before or overlap with STEP’09 • CASTOR v.2.1.8 already deployed • The transfer rate test will be coupled with first pass reco@T0 and second pass reco@T1

  23. Grid operation – site support • We need more help from the regional experts and site administrators • Proactively looking at local services problems • With data taking around the corner, the pressure to identify and fix problem will be mounting • STEP09 will hopefully demonstrate this (albeit for a short time) • The data taking will be 9 months of uninterrupted operation!

  24. Grid operation – site support • Two day training session on 26/27 May • VO-box setup and operation (gLite and AliEn services) • Common problems and solutions • Monitoring • Storage • The training will be also on EVO • All regional experts and site administrators are strongly encouraged to participate • More than 40 people have registered already

  25. Summary • Grid operation/middleware • The main focus is on reliable storage – not yet there • After initial ‘teething’ pains, the WMS is under control • CREAM CE must be everywhere and operational before data taking • In general, everyone needs services which ‘just run’, with minimal intervention and debugging • Grid operation/expert support • STEP’09 is the last ‘large’ exercise before data taking • Still, it will show only if there are big holes • The long LHC run will put extraordinary load on all experts • Training is organized for all – current status of software and procedures

More Related