1 / 21

The LHCb Tier-2 at INFN

The LHCb Tier-2 at INFN. Domenico Galli, Bologna. INFN CCRWS06 Otranto, 7.6.2006. Outlook. The LHCb data flow Aim of LHCb Tier-2s Why LHCb Analysis at Tier-1? Why LHCb Italian Tier-2 at CNAF? LHCb Tier-2 Exploitation in the Forthcoming Years LHCb Tier-2 Size and Cost Overall remarks.

garnet
Download Presentation

The LHCb Tier-2 at INFN

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. The LHCb Tier-2 at INFN Domenico Galli, Bologna INFN CCRWS06 Otranto, 7.6.2006

  2. Outlook • The LHCb data flow • Aim of LHCb Tier-2s • Why LHCb Analysis at Tier-1? • Why LHCb Italian Tier-2 at CNAF? • LHCb Tier-2 Exploitation in the Forthcoming Years • LHCb Tier-2 Size and Cost • Overall remarks The LHCb Tier-2 at INFN. 2 Domenico Galli

  3. CERN On-line Farm MC calibration data Selected DST+RAW TAG RAWmc data RAW data • CERN • Tier-1s Physics Analysis reconstruction User DST n-tuple User TAG rDST Local Analysis pre-selectionanalysis • Tier-3s Paper DST+RAW TAG The LHCb Dataflow • Tier-2s • On-line Farm • CERN • Tier-1s • CERN • Tier-1s Chaotic job Scheduled job The LHCb Tier-2 at INFN. 3 Domenico Galli

  4. The LHCb Dataflow (II) The LHCb Tier-2 at INFN. 4 Domenico Galli

  5. Aim of LHCb Tier-2s • In the LHCb Computing Model Tier-2s are used (at least in countries also provided with a Tier-1) as a purecentrally scheduled Monte Carlo simulation facility. • In the LHCb Computing Model Analysis is not performed on Tier-2s. • A LHCb Tier-2 consists in a PC-farm with a small disk buffer (3 TB in steady state) used as a temporary cache until data transfer to Tier-1. • LHCb-Italy proposes to build 1 Tier-2 hosted at Bologna-CNAF, together with Italian Tier­1. The LHCb Tier-2 at INFN. 5 Domenico Galli

  6. Why LHCb Analysis at Tier-1? • LHCb analysis jobs consist in selecting the events (stripped DST) stored at Tier-1 to focus on one particular analysis channel: • Typical analysis jobs run on a~106 event sample. • Some analysis jobs will run ona larger ~107 event sample. • Average event reduction of a factor of 5. • Analysis input is completely stored at each Tier-1. • Analysis output (20-200 GB) can be processed by a small Tier-3 facility. Available at each Tier-1 Available at each Tier-1 SelectedDST+RAW119 TB Event TagCollection20 TB Physics Analysis n-tuple / User DST + User TAGTypical: 20 GB Large: 200 GB Local Analysis The LHCb Tier-2 at INFN. 6 Domenico Galli Paper

  7. Tier-1 Tier-2 139 TB Output 20-200 GB DST+RAW+TAG139 TB 139 TB Buffer LAN WAN Tier-1 Output 20-200 GB DST+RAW+TAG139 TB 139 TB Why LHCb Analysis at Tier-1? (II) • Comparison between 2 models: • Analysis job at Tier-2: • Analysis job at Tier-1: • Data accessed at Tier-1 per analysis job are the same. • But the second is faster and less expensive in terms of hardware, infrastructure, staff resources and WAN load. LAN The LHCb Tier-2 at INFN. 7 Domenico Galli

  8. Why Tier-2 at CNAF? • This model would allow maximum flexibility in moving resources back/forth between Tier-2 and Tier-1 to optimize resource exploitation. (to satisfy peak MC/analysis request). • Simply by means of a software operation. • No competition among Italian sites on Tier-2 resources, since MC production is centrally scheduled. • Italian LHCb people involved in computing are mainly located in Bologna. The LHCb Tier-2 at INFN. 8 Domenico Galli

  9. Why Tier-2 at CNAF? (II) • LHCb experiment staff from Bologna • Already heavily involved in LHCb computing; • Established strict collaboration with the CNAF staff. • Same trained and skilled management and technical staff. • Given the growing profile, LHCb Tier-2 is at maximum a +10% perturbation of CNAF Tier-1 resources. • Same building. • Same cooling system. • Same fire alarm and surveillance. • Same network. • Same electric power and UPS. • Etc. The LHCb Tier-2 at INFN. 9 Domenico Galli

  10. LHCb Tier-2 Exploitation in the Next Years • From now on, practically speaking, an almost continuous MC production is foreseen for LHCb. Mainly for: • Physics studies; • HLT studies. • Order of 100's Mevents/year. The LHCb Tier-2 at INFN. 10 Domenico Galli

  11. LHCb Tier-2 Size and Cost • We are sizing the Italian Tier-2 to be 15% of the total Tier-2 resources of the whole LHCb collaboration. • 15% = Italian fraction of CORE funds; • 15% = fraction of Italian physicists with respect of the total involved in the LHCb experiment. The LHCb Tier-2 at INFN. 11 Domenico Galli

  12. LHCb Tier-2 (@CNAF): Additional Size and Cost (according to LHCb Computing Model) 3.2 GHz Xeon = 1.2 kSi2k The LHCb Tier-2 at INFN. 12 Domenico Galli

  13. LHCb Tier-2 (@CNAF): Additional Infrastructures Power consumption: 50 W/kSi2k in 2006 25 W/kSi2k in 2010 70W/TiB The LHCb Tier-2 at INFN. 13 Domenico Galli

  14. LHCb Tier-1/Tier-2 at INFN Comparison The LHCb Tier-2 at INFN. 14 Domenico Galli

  15. 3.2 CERN Tier-1 INFN Tier-2 INFN 3.2 DT: 50/50/72 RP: 168/232/232 STR: 120/120/120 DT: 88/88/176 RP: 176/480/480 STR: 608/608/608 6.4 Other Tier-1s LHCb-INFN Network Bandwidth • Throughput in Mb/s for the years 2008/2009/2010. • DT: Data Taking; • RP: Reprocessing: winter shut-down (2 months); • STR: Re-stripping: 3 times in a year: after data taking (1 month), after reprocessing (2 months), before next year data taking (1 month). The LHCb Tier-2 at INFN. 15 Domenico Galli

  16. LHCb software need at Tier-2 • The functioning of LHCb Tier-2s is well-known, since they only perform Monte Carlo production. • Already at the start-up of Tier-1 the LHCb Bologna group set up a farm for MC production. • No I/O intensive. • Services to be implemented includes CE, SE, RB, G-PBox. • Tier-2s are not technically critical in LHCb: • They only have to produce the required amount of MC data. The LHCb Tier-2 at INFN. 16 Domenico Galli

  17. Overall remarks • On October 10, 2005, LHCb requested to the CSN1 the resources allocation for the Tier-2 at CNAF. • The request was partly (100 k€) approved sub-judice by CSN1, but availability of these resources is now bound to the resolution of general CNAF infrastructure problems. • Problem fixing could take a while. In the meantime LHCb needs resources for Monte Carlo productions. • Till now LHCb has made up for its lack of dedicated resources with the exploitation of the unused INFN-Grid resources. • If the exploitation policy of Tier-2 resources will not be closedandcomputing resources will continue to be available for LHCb then no further problems will arise, waiting for the CNAF problems to be fixed. The LHCb Tier-2 at INFN. 17 Domenico Galli

  18. Overall remarks (II) • The Tier-1 center must work. • Infrastructural and organizational problems must be resolved. • The Tier-2 federation could not make up for the Tier-1 malfunctioning. • In the last 5 years the Tier-1 personnel has learnt a skill that other centers would take few years to collect. • All seems simple until one comes up against scalability problems. • The need of dedicated personnel cannot be set aside. • This will be more evident during steady state. In the set-up phase there are many mobilized troops that in steady state will be missing. Job efficiency The LHCb Tier-2 at INFN. 18 Domenico Galli

  19. Overall remarks (III) • In order for the Tier-2 federation to work efficiently: • A Tier-2 coordination must exist above the sites and the experiments. • A policy enforcement mechanism (G-PBox) must work. • Otherwise we could have simultaneously unused resources together with resource lack. The LHCb Tier-2 at INFN. 19 Domenico Galli

  20. Overall remarks (IV) • At the Tier-1 (as well as for the other experiments at the Tier2s) LHCb needs very performing disk storage solutions for analysis jobs. • High availability and high I/O throughput; • Possibility to access files on the SE using a “file” protocol: • i.e. without copying the file from/to the local disk; • we would not like to rely on the local disks of the WNs at all! • Dynamic management of disk storage allocation: • lifetime, pinning, space pre-allocation provided by SRM-v2, • see G. Donvito and A. Forti at this workshop for the status with SRM-v2. • Various solutions on the market, each one with its pro’s and con’s, the perfect product does not exist yet! The LHCb Tier-2 at INFN. 20 Domenico Galli

  21. Overall remarks (V) • LHCb-INFN investigated, together with CNAF, the parallel file systems (GPFS, Lustre) as a valuable solution, if provided together with an appropriate SRM-v2, e.g. StoRM (developed by INFN/EGRID) • Works at lower level; • Less increase of complexity with scale; • Less maintenance/configuration needs. • See V. Sapunenko and A. Brunengo at this workshop. • Other valuable solutions include: dCache, DPM, xrootd: • Developed respectively in US/DESY, CERN, US (the latter also with a developer from INFN-Padova). The LHCb Tier-2 at INFN. 21 Domenico Galli

More Related