XCache Server

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XCACHE Server at LRZ

An alternative way to access arbitrary ATLAS data (registered in RUCIO) is via the xcache server at LRZ.

  • xcache is a caching system based on xrootd which communicates with Rucio to find and download arbitrary files.
  • It supports block-wise caching, so when reading a file with ROOT only the required blocks are downloaded.
  • It runs on a storage server lcg-lrz-xcache0.grid.lrz.de at LRZ (former dCache pool node)



Xcache supports both full physical filenames (protocol:server-name:pathname) (so-called TURL, protocol should be root or http)

root://lcg-se0.ifh.de:1094//pnfs/ifh.de/data/atlas/atlasdatadisk/rucio/mc16_13TeV/fd/5f/DAOD_EXOT4.12553107._000027.pool.root.1


and logical Rucio names (scope:filename)

/atlas/rucio/mc16_13TeV:DAOD_EXOT4.12553107._000027.pool.root.1

To access the files via xcache one has to prepend:

root://lcg-lrz-xcache0.grid.lrz.de:1094

( root-protocol:server-name:port )

Please note: You need a valid ATLAS voms-proxy to access the LRZ xcache server!




Usage examples:

Download whole file with xrdcp (xrootd copy, available with ATLAS release after lsetup rucio)

# using full TURL
xrdcp -d 2 -f root://lcg-lrz-xcache0.grid.lrz.de:1094//root://lcg-se0.ifh.de:1094//pnfs/ifh.de/data/atlas/atlasdatadisk/rucio/mc16_13TeV/fd/5f/DAOD_EXOT4.12553107._000027.pool.root.1 /scratch-local/$USER
#
# using logical file name:
xrdcp -d 2 -f root://lcg-lrz-xcache0.grid.lrz.de:1094//atlas/rucio/mc16_13TeV:DAOD_EXOT4.12553107._000027.pool.root.1 /scratch-local/$USER


Open File directly in ROOT :

root -l
# full TURL
root [0] TFile * f = TFile::Open("root://lcg-lrz-xcache0.grid.lrz.de:1094//root://fax.mwt2.org:1094//pnfs/uchicago.edu/atlasdatadisk/rucio/data17_13TeV/15/b6/DAOD_SUSY6.13027526._000305.pool.root.1")
#
# or logical FN
root [0] TFile * f = TFile::Open("root://lcg-lrz-xcache0.grid.lrz.de:1094//atlas/rucio/data17_13TeV:DAOD_SUSY6.13027526._000305.pool.root.1")



Add-on: Rucio commands:

# list logical filenames fordataset
rucio list-files data17_13TeV:data17_13TeV.00328099.physics_Main.deriv.DAOD_SUSY6.f836_m1824_p3402_tid13027526_00
#
# list physical filenames for replica available with root protocol
rucio list-file-replicas --protocol root data17_13TeV:data17_13TeV.00328099.physics_Main.deriv.DAOD_SUSY6.f836_m1824_p3402_tid13027526_00
#
# gives all replicas at all RSEs, better restrict to one:
rucio list-file-replicas --rse UNI-FREIBURG_DATADISK --protocol root data17_13TeV:data17_13TeV.00328099.physics_Main.deriv.DAOD_SUSY6.f836_m1824_p3402_tid13027526_00