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DCache Basics

DCache Basics. Alessandro Usai, Sergio Maffioletti Grid Group CSCS. DCache General Architecture. DCache is flexible. At the core of DCache are subservices (cells) and domains (JVM) sub-services can run in different locations. General comments.

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DCache Basics

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  1. DCache Basics Alessandro Usai, Sergio Maffioletti Grid Group CSCS

  2. DCache General Architecture

  3. DCache is flexible • At the core of DCache are subservices (cells) and domains (JVM) • sub-services can run in different locations

  4. General comments • It is all Java based i.e. platform independent (in principle) • It is highly configurable (good) but complex (bad)…the documentation could (needs to) be improved, the logs are obscure (if not absent, unless you explicitly increase the debug level) • Not easy to maintain upgrades • Yaim component not powerful enough (i.e. you do it by hand)

  5. DCache@CSCS

  6. In a nutshell • Pnfs needs to be mounted by the pool and admin nodes (they need to be authorized) • Postgres configured to grant the admin node • Thumpers installed by coping /opt/d-cache from the admin node and changing the configuration where required. Data and Control dirs are placed under /data1 and pointed to via sym links • CAs and grid-mapfile regular update from CE (via cronjob)

  7. Our Pools Configuration • Read only and write only pools (to balance the load) • p2p enabled (files are replicated for load reasons, only cache copies which get deleted if needed) • Two movers queues: wan (gridftp) and default (dcap) • 10 concurrent transfers at a time • se02-lcg with dteam+ops,cms,atlas and se03-lcg with dteam+ops,cms,atlas,lhcb,hone,dech

  8. Some problems we saw • Logging obscure (difficult to troubleshoot) • Domains duplication (as a result we got on board default configuration and a performance hit) • Timeouts (a known problem still under investigation within the community) • Various authentication problems due to misconfigurations (e.g. wrong VO tags)

  9. How are we doing just now?

  10. Tips and Advices • Recommended: increase the logging level • Install srmwatch (beware of the security holes though) • Get acquainted with the ssh interactive shell on the admin node (ssh -l admin -c blowfish -p 22223 localhost) • The dcache admin web page is very useful (http://storage01-lcg.projects.cscs.ch:2288/) • In case off problems user-forum@dCache.ORG

  11. References • http://twiki.cscs.ch/twiki/bin/view/LCGTier2/CSCSDCACHE_ausai • http://www.dcache.org/ • http://www.dcache.org/manuals/workshop2007/ndgf.shtml

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