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Experiences of DCache at RAL UK HEP Sysman, 11/11/04

Explore the evolution of DCache at RAL, from origins and current deployments to unanswered questions and the need for improved documentation.

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Experiences of DCache at RAL UK HEP Sysman, 11/11/04

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  1. Experiences of DCache at RALUK HEP Sysman, 11/11/04 Steve Traylens.traylen@rl.ac.uk

  2. DCache Origins • Developed and maintained by Fermilab and DESY. • Used extensively by Zeus/H1 at DESY. • Designed primarily to sit in front of a tape store.

  3. Why DCache • Gives you a virtual filesystem across many file systems optionally on several nodes. • Allows replication within filesystem to increase redundancy. • Allows a tape system to be interfaced at the back to increase redundancy further. • Data protocols are scalable, one GridFTP interface per server is easy and transparent.

  4. DCache Doors • Doors can be created into the system. • GridFTP • SRM • GSIDCAP • A POSIX interface is available to this. • All of these are GSI enabled but Kerberos doors also exist. • Everything remains consistent regardless of the door that is used. • A big advantage over the edg-se.

  5. History of DCache at RAL • Mid 2003 • We deployed a non grid version for CMS. It was never used in production. • End of 2003/Start of 2004 • RAL offered to package a production quality DCache. • Stalled due to bugs and went back to developers and LCG developers.

  6. DCache today at RAL • September 2004 • Redeployed DCache into LCG system for CMS and DTeam VOs. • In production, yet to be proved. • Deployed within JRA1 testing infrastructure for gLite i/o daemon testing.

  7. Current Deployment at RAL

  8. Transfer into DCache

  9. Transfer into DCache

  10. Upcoming Deployments • Both LHCb and Atlas want a DCache setup. • This is happening now. • LHCb also wants the system backed to the ADS. • At this time this has not been investigated but will be by the tier1 or the storage group.

  11. Extreme Deployment.

  12. Current Installation Technique • The tier1 now has its own cookbook to follow but is not generic at this time. • Prerequisites • VDT for certificate infrastructure. • edg-mkgridmap for grid-mapfile. • J2RE. • Host certificate for all nodes with a GSI door.

  13. RPM Packages • Head NODE • d-cache-client, d-cache-lcg, d-cache-core, d-cache-opt and pnfs • Pool NODE • d-cache-lcg and d-cache-core.

  14. Configuration • Change a few files and run some scripts with arguments. • The scripts do a lot so fixing any problems at this stage is difficult and has required expert help.

  15. Comments • Documentation is severely lacking for the operation of DCache. • E.g There is admin interface accessible via ssh where pools can be marked read only, possibly drained,…. • Trial and error is the standard method. • With the LCG release a admin guide is promised.

  16. Unanswered Questions • How do we drain a node for maintenance? • CHEP papers suggest this is possible. • How do we use one dCache for multiple VOs? • Is there a concept of defining quotas for groups? • Can we tie one group to specific nodes.

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