GridStorageAccess

This page describes how to handle data stored on our mass storage system.

Introduction

T2B has an ever increasing amount of mass storage available. This system hosts both the centrally produced datasets as well as the user produced data.
The mass storage is managed by a software called dCache. As this software is in full development, new features are added continuously. This page contains an overview of the most used features of the software.

General info

As dcache was designed for precious data, the files are immutable. This means that once they are written, they cannot be changed any more. So, if you want to make changes to a file on dcache, you need to first erase it and then write it anew. Our dCache instance is mounted on all the M machines and can be browsed via the /pnfs directory. If you want to find your personal directory, the structure is the following:

• On the M machines /pnfs is mountes

Before starting

Before being able to run these commands you first need to make a valid proxy

voms-proxy-init --voms MYEXPERIMENT

Where MYEXPERIMENT is one of 'cms, icecube, beapps'

GFAL

GFAL is a wrapper around the latest grid commands. Learning to use it means that whatever middleware requires to be used in the future, you don't need to learn new commands (like srm, lcg, etc)

gfal-commands

If you want more information on the options that can be used, please use man gfal-command !

Here are all the commands that can be used:

• gfal-ls: get information on a file
• gfal-mkdir: remove a directory
• gfal-rm: removes a file. To remove an entire directory, use -r
• gfal-copy: copy files.

Usage

There are 2 types of file url:

• Distant files: their url is of the type srm://<name_of_server>:<port>/some/path, eg for IIHE:

srm://maite.iihe.ac.be:8443/pnfs/iihe/

• Local files: their url is of the type file://path_of_the_file, eg for IIHE:

file:///user/$USER/MyFile.root

Be careful, the number of / is very -very- important

• To get a list of all distant urls for all the Storage Elements, one can do:

 lcg-infosites --vo cms se 

Examples

• To list the contents of a directory /pnfs/iihe/cms :

 gfal-ls srm://maite.iihe.ac.be:8443/pnfs/iihe/cms 

• To create a directory:

 gfal-mkdir srm://maite.iihe.ac.be:8443/pnfs/iihe/cms/store/user/$USER/NewDir 

• copy file from local disk to remote server

 gfal-copy file:///user/$USER/MyFile.root srm://maite.iihe.ac.be:8443/pnfs/iihe/cms/store/user/$USER/ 

• To copy a file from remote server to our Storage Element:

 gfal-copy srm://srm-eoscms.cern.ch:8443/srm/v2/server?SFN=/eos/cms/store/group/comm_trigger/L1TrackTrigger/BE5D_620_SLHC6/singleMu/NoPU/reDIGI_SLHC6-TrackTrigger_muon_pgun-0499.root srm://maite.iihe.ac.be:8443/pnfs/iihe/cms/store/user/odevroed/eosTransfer.root 

• To delete a file on remote server

 gfal-rm srm://maite.iihe.ac.be:8443/pnfs/iihe/cms/store/user/$USER/MyFile.root 

• To remove a directory and its entire content on remote server ?!? not working for now ?):

 gfal-rm -r srm://maite.iihe.ac.be:8443/pnfs/iihe/cms/store/user/$USER/NewDir 

Bulk file transfers

There is an elegant way to run gfal-copy through several files. This is done using the --from-file option.

Syntax:

 gfal-copy -f --from-file files.txt file://$PWD 

where files.txt is a file where every line is a source in srm url syntax.

Make some tests with one line in datafile and make sure the srm url is OK for both source and destination before running over several files.

Copy directories from and to pnfs within the IIHE

A script to copy full directories to and from pnfs exists on the slc6 UI's:

copyDirectoryPnfs.py
Move all files in a directory to or from pnfs
This script assumes that you copy within the IIHE
The script does not do recursive copying
Make sure you have a valid proxy, made with voms-proxy-init --voms cms:/cms/becms

Mandatory options:
--in=                 : directory to copy from
--out=                : directory to copy to
Both directories need to be complete (i.e. including the /pnfs or /user part

example:
copyDirectoryPnfs.py --out=/user/odevroed/newfile --in=/pnfs/iihe/cms/store/user/odevroed/newdir

Optional:
-h, --help             : print this help message

dCache

Direct dcache access to files is only possible if the software supports it. PNFS (the directory structure seen under /pnfs/) is NOT a real filesystem: it is an immutable filesystem, and is mounted read-only.

• Therefore, here is a list of the commands that work:

ls

• And replacement commands:
  • dccp: to copy files from /pnfs to local disk. Example:

dccp dcap://maite.iihe.ac.be/pnfs/iihe

• To open files using root, use eg

 root dcap://maite.iihe.ac.be/pnfs/iihe/some/file.root 

When reading out the rootfiles is rather slow or it doesn't work at all and nothing is wrong with the root file (e.g. in an interactive analysis on beo or msa) you can increase your dCache readahead buffer. Don't make the buffer larger than 50MB! To enlarge the buffer set this in you environment :
For csh:

setenv DCACHE_RAHEAD 1
setenv DCACHE_RA_BUFFER 50000000

For bash:

export DCACHE_RAHEAD=true
export DCACHE_RA_BUFFER=50000000

See the dChache fanpage for further reading.