GridPP Tier-2 experiences of dCache Greig A. Cowan University of - - PowerPoint PPT Presentation

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GridPP Tier-2 experiences of dCache Greig A. Cowan University of - - PowerPoint PPT Presentation

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GridPP Tier-2 experiences of dCache Greig A. Cowan University of Edinburgh I V N E U R S E I H T Y T O H F G R E U D B I N Greig A Cowan dCache workshop January 2007 Outline 1. What is a GridPP Tier-2? 2. GridPP

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GridPP Tier-2 experiences of dCache

Greig A. Cowan University of Edinburgh

T H E U N I V E R S I T Y O F E D I N B U R G H

Greig A Cowan dCache workshop January 2007

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SLIDE 2

Outline

  • 1. What is a GridPP Tier-2?
  • 2. GridPP experiences

(a) Configuration, administration, monitoring

  • 3. Some comments
  • 4. Summary

Greig A Cowan dCache workshop January 2007

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What is GridPP?

  • UK Grid for particle physics.
  • Large computing facility (Tier-1) at Rutherford Appleton Laboratory (RAL).
  • 19 geographically distinct Tier-2 sites.

Greig A Cowan dCache workshop January 2007

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What is a Tier-2?

In terms of storage, they can typically be characterised by:

  • No tape backend.
  • Relatively small amount of RAID5 disk (∼10-100TB).
  • Single dCache head node and a few pool/door nodes.
  • 1GbE external + internal connectivity.
  • Resources may have to be shared with non-HEP users.
  • Limited manpower (∼1 FTE).

– Ease of configuration, management and monitoring are essential to maximise avail- ability.

Greig A Cowan dCache workshop January 2007

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dCache in GridPP

Site Disk Site Disk Edinburgh 20TB Lancaster 60TB RAL-PPD 20TB Manchester 250TB IC-HEP/IC-LeSC 50TB Liverpool 7TB

  • 12 (generally) smaller sites use DPM.
  • A lot of experience:

http://www.gridpp.ac.uk/wiki/DCache

Greig A Cowan dCache workshop January 2007

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dCache in GridPP

  • Extensive testing of Tier-2 infrastructure.

– dCache plays major part.

Greig A Cowan dCache workshop January 2007

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Configuration

  • YAIM used for initial basic installation.
  • Admin typically performs final tweaks by hand. i.e., adding extra pools, pool groups,

units, links. . .

  • Integration of dCache with YAIM has improved greatly over the past 6 months.

– Different pool and admin meta-packages. – Dedicated DESY repository. – Small incremental releases good.

∗ Although apt auto-update can break your install!

http://www.gridpp.ac.uk/wiki/DCache Yaim Install

Greig A Cowan dCache workshop January 2007

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Manchester

  • Batch farm of 900 WNs , each with >250GB disk.
  • Each WN running dcache-pool.
  • 45 gridftp doors.
  • Partitioned into two dCache’s to ease management.
  • Configuration with cfengine

http://www.cfengine.org – Central repo of config files (dCacheSetup, node config) – Node pulls in new config file if changed. – Not able to restart services yet.

  • Resilient dCache NOT currently being used.

– Testbed setup for evaluation.

Greig A Cowan dCache workshop January 2007

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xrootd door

  • RAL-PPD has deployed the xrootd door in read only mode.
  • Initial tests showed that basic functionality was working.
  • Chris Brew heavily involved in BaBar computing.
  • Has since included dcap support in BaBar software so xrootd not used significantly.

Greig A Cowan dCache workshop January 2007

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OBSERVATIONS

Greig A Cowan dCache workshop January 2007

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CLOSE WAIT

Edinburgh Lancaster

  • Eventually door stops working.

java.lang.OutOfMemory gPlazma diskCacheV111.services.authorization.AuthorizationServiceException

  • Everything else is functioning.
  • Typical netstat output (29107 is the gridftp door process):

tcp 1 0 pool1.epcc.ed.ac.uk:2811 fts106.cern.ch:20009 CLOSE WAIT 29107/java

Greig A Cowan dCache workshop January 2007

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Log messages

  • dCache logs remain cryptic .

– Solution is often to restart the service. Is there a better way?

  • Tomcat logs filled up root partition of Lancaster SRM node.

– 5GB! – Tomcat logs in a different place from dCache and PNFS logs. https://www.gridpp.ac.uk/wiki/DCache Log Message Archive

Greig A Cowan dCache workshop January 2007

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Admin tools

  • Namespace ↔ disk pool synchronisation .

– People often find ghost files on disk or in PNFS. – Would like to identify discrepancies and fix them.

  • Admin shell is really not user friendly.

– Could we share scripting tools that individual sites have developed? – Would like to find out about the jpython interface.

Greig A Cowan dCache workshop January 2007

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CURRENT WORK

Greig A Cowan dCache workshop January 2007

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Storage accounting

  • System deployed in UK. Accounting for EGEE.
  • Uses information in the global BDII .
  • Difficult to account storage if VOs share disk pools.

– GridPP have own GIP plugin (du on /pnfs).

∗ Unable to query database. Chimera?

http://www.gridpp.ac.uk/wiki/GridPP dCache GIP plugin

Greig A Cowan dCache workshop January 2007

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Current work

  • Stress testing dcap access from batch farm.

– Do we need separate read/write pools? File hopping?

  • ScotGrid distributed dCache .

– Storage at Edinburgh and Glasgow. – Use lightpath between sites. – Single SRM for the entire Tier-2 cluster → simpler to manage with shared support?

  • Monitoring

– See talk tomorrow.

Greig A Cowan dCache workshop January 2007

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Summary

  • Good understanding within GridPP of how to setup basic Tier-2 SRM (see wiki).

– Still gaining experience in setting up a large site (100’s of nodes and TB’s).

  • dCache is a key component of the SRM landscape in the UK.
  • Problems difficult to debug due to logfiles .
  • Further investigation of local access to the storage is needed.
  • Improved monitoring would be beneficial to community.

Greig A Cowan dCache workshop January 2007