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Storage Element Status

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  1. Storage Element Status GridPP7 Oxford, 31 June – 02 July 2003

  2. Contents • What is an SE? • The SE Today • What will it provide Really Soon Now™? • What is left for future developments?

  3. What is the Storage Element?

  4. Collaborations • DataGrid Storage Element • Integrate with WP2 Data Replication Services (Reptor, Optor) • Jobs running on worker nodes in a ComputingElement cluster may read or write files to an SE • SRM – Storage Resource Manager • Collaboration between Lawrence Berkeley, FermiLab, Jefferson Lab, CERN, Rutherford Appleton Lab

  5. EU DataGrid Storage Element • Grid Interface to Mass Storage Systems (MSS) • Flexible and extensible • Provides additional services for underlying MSS • E.g. access control, file metadata,…

  6. Control Interface • E.g. • cache file: stage file in from mass storage and place in disk cache • register existing file • SRM style interface • Interface was written before we had the SRM v.1 WSDL • Web service interface

  7. More about SRM • Users know Site File Names (SFN) or Physical File Names (PFN) • SE cache file request id Disk cache MSS file

  8. More about SRM • Client queries the status of a request • Better that client polls than server callbacks • Server (ideally) able to give time estimate SE status? “not ready, try later” Disk cache MSS file

  9. More about SRM • When request is ready, client gets a Transfer URL (TURL) • gsi SE status? ready: TURL Disk cache MSS file file

  10. More about SRM • Client accesses the file in the SE’s disk cache using (usually) non-SE tools SE Disk cache MSS globus- url-copy file file file

  11. More about SRM • Finally, client informs SE that data transfer is done • This is required for cache management etc SE done ok Disk cache MSS file file

  12. Data transfer interface • GridFTP • The standard data transfer protocol in SRM collaboration • Some SEs will be NFS mounted • Caching and pinning still required before the file is accessed via NFS • Easy to add new data transfer protocols • E.g. http, ftp, https,…

  13. Information Interface • Can publish into MDS • Can publish (via GIN) R-GMA • Using GLUE schema for StorageElement • • Also a file metadata function as part of the control interface

  14. The SE Today

  15. Implementation • XML messages passed between applications • Functionality implemented in handlers • A handler is a specialised program reading a message, parsing it, and returning a message • Each handler does one specific thing

  16. Handlers processing request Request Manager Handler 1 User lookup Handler 2 File lookup Handler n Return Time

  17. Architecture handler3 handler4 handler5 Global Data handler1 handler2 request • The request contains the sequence of names of handlers • As each handler processes the request, it calls a library that moves the name to an audit section • The library allows easy access to global data • Handlers may also have handler-specific data in the XML • Storing the XML output from each handler as the request gets processed makes it easy to debug the SE sequence XML audit

  18. Mapping to local user • SE runs as unprivileged user with a highly constrained setuid executable to map to local users • Mapping done using gridmap file, using pooled accounts if available • Needed for access to some (many) mass storage systems

  19. Deployment • MSS working CERN – Castor and disk RAL – Atlas DataStore and Disk • Testing HPSS via RFIO (CC-IN2P3) ESA/ESRIN testing disk, then plan tape MSS (AMS) NIKHEF disk • Others SARA building from source on SGI INSA/WP10 – to build support for DICOM servers UAB Castor – testing

  20. Installation • RPMs and source available • Source compiles with gcc 2.95.x and 3.2.3 • Configures using LCFG-ng • Tools available to build and install Ses without LCFG: ./configure –mss-type=disk make make install

  21. Roadmap

  22. Priorities for September • WP2 TrustManager adopted for security but need to LCFG configure • Currently building proper queuing system • SRM v.1.1 interface • Access control – use GACL • Improved disk cache management (including pinning) • VOMS support • SRM v2.1 interface (partial support)

  23. Future developments

  24. Future Directions • Guaranteed reservations • SRM2 recommendations: volatile, durable, permanent files and space • Full SRM v2.1 • Scalability • Scalability will be achieved by making a single SE distributed • Not hard to do