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SBND dCache storage » History » Version 7

Gianluca Petrillo, 12/08/2017 02:26 PM

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h1. SBND dCache storage
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{{>toc}}
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dCache area consists of a huge data space, made of tapes and disks.
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SBND owns one of each of two types of dCache areas. Each of them has room for areas owned by a single user:
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* scratch (@/pnfs/sbnd/scratch/users/${USER}@): files in this area can be deleted automatically; you can store a grid job result there waiting to transfer it into a safe place, but don't rely on leaving your important stuff there for long
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* persistent (@/pnfs/sbnd/persistent/users/${USER}@): files in this area will not be deleted
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We have a limited quota of space as well, so fill it responsibly.
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|. @/pnfs/sbnd/persistent@ | 37.6 TiB (20170915)       |
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|. @/pnfs/sbnd/scratch@    | 81.3 TiB (20171001)       |
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("check the persistent space monitoring...":https://fifemon.fnal.gov/monitor/dashboard/db/dcache-persistent-usage-by-vo?orgId=1&var-VO=sbnd)
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More details are in [[fife:Understanding storage volumes|FIFE wiki]].
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h2. Remote access to dCache areas
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While dCache areas may happen to be available on some local nodes (e.g., [[Computing resources#Where-to-work-interactive-nodes-GPVM|SBND GPVM's]]), in general the area is not directly reachable.
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We use a tool called [[ifdhc:|IFDH]] to fetch files from wherever they are. Also some code uses IFDH to fetch files: among them, LArSoft modules @CORSIKAGen@ and @GENIEGen@.
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IFDH sometimes requires the user to be _authenticated_, which is usually achieved by a certificate.
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This is the [[Get a certificate proxy|same procedure]] as for getting credentials to submit jobs.
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h3. Use XRootD to access dCache ROOT files
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Even where @/pnfs@ directory structure is actually visible, it is usually a bad idea to access ROOT files from there directly. A better practice is using, when possible, access via XRootD:
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# have a grid proxy available
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# use a XRoodD URL instead of a @/pnfs@ path; a script to perform such a conversion is provided in LArSoft as @pnfsToXRootD@ (larsoft:source:bin/pnfsToXRootD, installed in the system @PATH@ and in @${LARSOFT_DIR}/bin@)
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For example, instead of:<pre>$ lar -c standard_g4_sbnd.fcl -s /pnfs/sbnd/persistent/sbndpro/SBNWorkshop1017/v06_53_00_SBNWorkshop1017/prodsingle_mu_bnblike/gen/546347_0/prodsingle_sbnd_SinglesGen-20171018T115050_3cc94721-f58b-401f-806c-5fe63cf2bba8.root</pre>one can go:<pre>$ pnfsToXRootD /pnfs/sbnd/persistent/sbndpro/SBNWorkshop1017/v06_53_00_SBNWorkshop1017/prodsingle_mu_bnblike/gen/546347_0/prodsingle_sbnd_SinglesGen-20171018T115050_3cc94721-f58b-401f-806c-5fe63cf2bba8.root
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root://fndca1.fnal.gov:1094/pnfs/fnal.gov/usr/sbnd/persistent/sbndpro/SBNWorkshop1017/v06_53_00_SBNWorkshop1017/prodsingle_mu_bnblike/gen/546347_0/prodsingle_sbnd_SinglesGen-20171018T115050_3cc94721-f58b-401f-806c-5fe63cf2bba8.root
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$ lar -c standard_g4_sbnd.fcl -s root://fndca1.fnal.gov:1094/pnfs/fnal.gov/usr/sbnd/persistent/sbndpro/SBNWorkshop1017/v06_53_00_SBNWorkshop1017/prodsingle_mu_bnblike/gen/546347_0/prodsingle_sbnd_SinglesGen-20171018T115050_3cc94721-f58b-401f-806c-5fe63cf2bba8.root</pre>or, in one line:<pre>$ lar -c standard_g4_sbnd.fcl -s "$(pnfsToXRootD /pnfs/sbnd/persistent/sbndpro/SBNWorkshop1017/v06_53_00_SBNWorkshop1017/prodsingle_mu_bnblike/gen/546347_0/prodsingle_sbnd_SinglesGen-20171018T115050_3cc94721-f58b-401f-806c-5fe63cf2bba8.root)"</pre>