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SBND dCache storage » History » Version 1

Gianluca Petrillo, 09/26/2016 01:52 PM

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h1. SBND dCache storage
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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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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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The ritual for getting the required authorisations goes like this:
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<pre>kinit "${USER}@FNAL.GOV"                                                     # get your Kerberos authentication
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kx509                                                                        # ask Kerberos for a x509 certificate
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voms-proxy-init -noregen -rfc -voms 'fermilab:/fermilab/sbnd/Role=Analysis'  # create a "proxy" from the certificate</pre>
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The last line of the output from this sequence should look something like:
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<pre>Your proxy is valid until Tue Sep 27 01:49:24 2016</pre>
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where the date is 24 hours in the future. This "proxy" is what we need to get our job done.
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This is the same procedure as for getting credentials to submit jobs.