SBND dCache storage

dCache area consists of a huge data space, made of tapes and disks.
SBND owns one of each of two types of dCache areas. Each of them has room for areas owned by a single user:

  • scratch (/pnfs/sbnd/scratch/users/${USER}): files in this area can be deleted automatically; you can store a grid job result there waiting to transfer it into a safe place, but don't rely on leaving your important stuff there for long
  • persistent (/pnfs/sbnd/persistent/users/${USER}): files in this area will not be deleted

We have a limited quota of space as well, so fill it responsibly.

/pnfs/sbnd/persistent 37.6 TiB (20170915)
/pnfs/sbnd/scratch 81.3 TiB (20171001)

(check the persistent space monitoring...)
More details are in FIFE wiki.

Remote access to dCache areas

While dCache areas may happen to be available on some local nodes (e.g., SBND GPVM's), in general the area is not directly reachable.
We use a tool called IFDH to fetch files from wherever they are. Also some code uses IFDH to fetch files: among them, LArSoft modules CORSIKAGen and GENIEGen.

IFDH sometimes requires the user to be authenticated, which is usually achieved by a certificate.
This is the same procedure as for getting credentials to submit jobs.

Use XRootD to access dCache ROOT files

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:
  1. have a grid proxy available
  2. 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)

For example, instead of:

$ 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
one can go:
$ 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
$ lar -c standard_g4_sbnd.fcl -s root://
or, in one line:
$ 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)"