A request was made to me to send a synopsis of a problem we're having at Nebraska be sent to this list.
We're having a strange issue at Nebraska involving our xrootd redirector + opportunistic clusters.
Here's the problem:
Worker nodes on our tusker cluster (with names like cxxxx.tusker.hcc.unl.edu) will make a redirection request to our xrootd.unl.edu redirector. These requests fail even though the requested file may exist in our Nebraska CMS tier-2 storage. If a direct xrdcopy request from a worker to one of our xrootd doors the transfer works fine.
Broken attempt might look like:
xrdcp root://xrootd.unl.edu//store/mc/Fall13dr/QCD_Pt-30to50_Tune4C_13TeV_pythia8/GEN-SIM-RAW/castor_tsg_PU20bx25_POSTLS162_V2-v1/010000/D870A076-657D-E311-9A82-0025905A60B8.root /tmp/tes/CMSSW_7_1_2/teln.root
Last server error 3011 ('No reachable servers are available to read the file.')
But look at this:
xrdcp -x root://red-gridftp3.unl.edu//store/mc/Fall13dr/QCD_Pt-30to50_Tune4C_13TeV_pythia8/GEN-SIM-RAW/castor_tsg_PU20bx25_POSTLS162_V2-v1/010000/D870A076-657D-E311-9A82-0025905A60B8.root /tmp/tes/CMSSW_7_1_2/teln.root
Extreme Copy enabled.
Source #1 root://129.93.239.173:1094//store/mc/Fall13dr/QCD_Pt-30to50_Tune4C_13TeV_pythia8/GEN-SIM-RAW/castor_tsg_PU20bx25_POSTLS162_V2-v1/010000/D870A076-657D-E311-9A82-0025905A60B8.root
^Crootd] Total 1269.37 MB |=>..................| 5.04 % [58.2 MB/s]
Watching verbose copy attempts it appears that the redirection request also reaches out to fnal's xrootd redirector as well. These nodes are, naturally, behind a NAT but the doors and redirector can resolve the nodes directly.
I'm stumped. This looks like a redirection problem triggered by our particular network topology. I'm all certain that things used to work.
Carl Lundstedt
UNL
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