CMSSW Fallback
The patch attached to this page allows a CMSSW run to fallback from the normal TFC access to an xrootd-based URL.
Whenever an error occurs when opening a CMS file, the application will switch to the Xrootd service.
This is only tested on CMSSW_3_7_0 or later.
CMSSW Patches
Before you apply any patches, make sure you have your CMS environment set up correctly. From the CMSSW_3_7_x directory, do:
cmsenv
export CVSROOT=:pserver:anonymous@cmscvs.cern.ch:/cvs_server/repositories/CMSSW
Now, apply patches and build the new code:
addpkg IOPool/Input
addpkg FWCore/Services
/usr/bin/curl -k https://twiki.cern.ch/twiki/pub/Main/CmsIOFallback/cmssw_fallback.patch | patch -p0
scram b -j4 USER_CXXFLAGS="-g"
It might take 3-5 minutes depending on the speed of your computer.
Add the xrootd service to the CMSSW run
Add the following line to your CMSSW .py file:
process.source.fallbackUrl = cms.untracked.string("root://xrootd.unl.edu/")
You can run CMSSW as normal; whenever CMSSW runs into a file it can't open, it will start using the CMS Data Access Testbed.