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"

Add the xrootd service to the CMSSW run

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.