1. 1 ALICE Grid Status David Evans The University of Birmingham GridPP 14 th Collaboration Meeting Birmingham 6-7 Sept 2005

2. 2 The ALICE Experiment ALICE is one of the four main LHC experiments at CERN. ALICE is one of the four main LHC experiments at CERN. Only one dedicated to heavy-ion physics. Only one dedicated to heavy-ion physics. –Study of QCD under extreme conditions ~ 1000 collaborators ~ 1000 collaborators ~ 100 institutions ~ 100 institutions Birmingham is only UK institute involved Birmingham is only UK institute involved

3. 3 UK ALICE Birmingham only UK institute in ALICE Birmingham only UK institute in ALICE Small group but plays a vital role Small group but plays a vital role –Responsible for the design, construction, building and maintenance of Central Trigger Processor and Local Trigger Units. –Getting involved in physics exploitation. physics exploitation. –No surplus UK manpower available for Grid work (ALICE Gridd experts at CERN). »i.e. no UK ALICE Gridd experts.

4. 4 ALICE Requirements Data taking (each year) Data taking (each year) –1 month of Pb-Pb data ~ 1 PByte –Also p-p for rest of the year ~ 1 PByte Large scale simulation effort Large scale simulation effort –1 Pb-Pb event: ~ 24 hrs (1 GHz) Data Reconstruction Data Reconstruction Data analysis Data analysis Smaller Collaboration than ATLAS or CMS but similar computing requirements. Smaller Collaboration than ATLAS or CMS but similar computing requirements.

5. 5 Computing Requirements Data processing (pp) Data processing (pp) –Calibration & alignment – (quasi) online –First reconstruction pass during data taking »Establish overall properties quickly –Followed by tuning pass –Followed by second reconstruction pass Data processing (Pb-Pb) Data processing (Pb-Pb) –Calibration & alignment during data taking –First reconstruction pass ~ 4 months –Second reconstruction pass ~ 6 months

6. 6 Computing Requirements Monte Carlo Simulations Monte Carlo Simulations –pp data: generate similar amount of MC data ~10 9 events –Pb-Pb data: generate ~ 10 7 events (factor 10 less than real data)

7. 7 Profile of CPU requirements Total CERN T0 CERN T1 Ext Tier 1 Ext Tier 2 35 MSK2K Jan 07Sept 08 Nov 09

8. 8 Tier Hierarchy MONARC Model MONARC Model Cloud Model (Tier free) used Cloud Model (Tier free) used in ALICE data challenges (native AliEn sites – for LCG site we comply with Tier model) in ALICE data challenges (native AliEn sites – for LCG site we comply with Tier model) Tier 0 RAW data master copy Data reconstruction (1 st pass) Prompt analysis Tier 1 Copy of RAW reconstruction Scheduled analysis Tier 2 MC production Partial copy of ESD Data analysis

9. 9 ALICE Gridd - AliEn AliEn (ALICE Environment) – Grid framework developed by ALICE – used in production for > 4 years. AliEn (ALICE Environment) – Grid framework developed by ALICE – used in production for > 4 years. Based on WEB services and standard protocols. Based on WEB services and standard protocols. Built around open source code Built around open source code –Less than 5% is native AliEn code (mainly PERL). To date, > 500,000 ALICE jobs have been run under AliEn control worldwide. To date, > 500,000 ALICE jobs have been run under AliEn control worldwide.

10. 10 First implementation of Alice World Computing Model AliEn@GRID

11. 11 Old AliEn Framework 100% perl5 SOAP Local Site elements Central services User

12. 12 AliEn Pull Protocol One of the major differences between ALiEn and LCG grids is that AliEn uses the pull rather thanpush protcol. One of the major differences between ALiEn and LCG grids is that AliEn uses the pull rather thanpush protcol. EDG/Globus model: EDG/Globus model: ALiEn model: ALiEn model: userserver Resource Broker userserver Resource Broker job list

13. 13 Resource Broker Pull instead of traditional Push architecture Broker Authen Logger TransferBroker IS TransferOptimiser EDG/Globus

14. 14 EGEE / gLite ALICE is committed to using as much common grid applications as possible. ALICE is committed to using as much common grid applications as possible. In the framework of the EGEE project (EU funded grid project) middleware (gLite) is being developed. In the framework of the EGEE project (EU funded grid project) middleware (gLite) is being developed. –ALICE was playing a full role in this project – not so much now ! Changes have been made to make AliEn work with LCG Changes have been made to make AliEn work with LCG –E.g. changes to File Catalogue (FC) LFC (Local File Catalogue or LCG File Catalogue) –V0 Box at Tier 1 –Globus/GSI compatible authentication

15. 15 Analysis Core of ALICE computing model is AliRoot Core of ALICE computing model is AliRoot –Uses ROOT framework Couple AliEn with ROOT for Grid-based analysis. Couple AliEn with ROOT for Grid-based analysis. –Use PROOF – Parallel ROOT Facility –To the user its like using ROOT 4-tier architecture: 4-tier architecture: –ROOT client session, API server (AliEn + PROOF), Site PROOF master servers, PROOF slave servers.

16. 16 PROOF Each node has PROOF slave Each site has PROOF master server Uses pull protocol i.e. the slaves ask the master for work packets. Slower slaves get smaller work packets etc. Client API Server AliEn FC …. List of sites with data

17. 17 Authentication - SASL SASL is the Simple Authentication and Security Layer, a method for adding authentication support to connection-based protocols. SASL is the Simple Authentication and Security Layer, a method for adding authentication support to connection-based protocols. AliEn now has perl module with implementation GSSAPI AliEn now has perl module with implementation GSSAPI This allows us to This allows us to –Use all SASL authentication schemes –Use old AliEn authentication (token, AFS password, SSH) –Use X509 certificates and Globus/GSI (AliEn distribution now includes necessary Globus/GSI software) –Develop secure Peer-To-Peer File Transfers based on machine/protocol/user certificates and LDAP based configuration management

18. 18 Authentication Client Proxy Server Database LDAP Request methods List of methods SASL Authentication Checking if user exists Data X509(AliEn/Globus) PKI/RSA (ssh) Token (AliEn) AFS password Server

19. 19 Summary AliEn is a Grid framework developed by ALICE using 95% open source code (e.g SOAP) and 5 % AliEn specific (perl) code. AliEn is a Grid framework developed by ALICE using 95% open source code (e.g SOAP) and 5 % AliEn specific (perl) code. –Successfully used over past 3 years ALICE wishes to use as many common grid solutions as possible ALICE wishes to use as many common grid solutions as possible AliEn evolving to take into account EGEE/gLite framework and to work with LCG. AliEn evolving to take into account EGEE/gLite framework and to work with LCG. –New user interfaces being developed –PROOF for analysis being developed –Better authentication/authorisation being developed –Etc.