dCache

dCache is a disk-based distributed storage system with a unique tree structure. At CC-IN2P3, the dCache service provides access to local data via gateways depending on the protocol used, such as WebDAV, XRootD, GridFTP and SRM.

This service is interfaced with the HPSS service, so it can be used as a disk cache in front of a tape-based backend. But it can also be used as a pure disk storage service.

Today dCache hosts data from Virtual Organizations (VO) belonging to the LHC and EGI collaborations.

Data access

Access to data is possible after authentication by grid certificate with appropriate proxy, or by tokens for VOs who have configured their IAM.

Clients are available on compute or interactive servers. Otherwise, you need to install the gfal2-util package, which contains all the clients.

XRootD protocol allows direct reading of files, while WebDAV protocol allows files to be read from and written to dCache from the outside. Available ports for LHC experiments and EGEE are shown below.

LHCEGEE

XRootDWebDAV

• ATLAS: ccxrootdatlas.in2p3.fr

• CMS: ccxrootdcms.in2p3.fr

• LHCb: ccxrootdlhcb

Example of a file copy using the XRootD protocol:

% xrdcp root://ccxrootdatlas.in2p3.fr:1094//pnfs/in2p3.fr/data/atlas/atlasdatadisk/rucio/mc15_14TeV/0f/20/AOD.10073441._001377.pool.root.1 /scratch/testxrd

By GridFTP protocol

Allows file transfers to and from dCache. It will be gradually replaced by WebDAV.

Example of a command to transfer a local file to dCache:

% gfal-copy file:///scratch/<my file> srm://ccsrm.in2p3.fr:8443/pnfs/in2p3.fr/data/dteam/<my file>

Example of a command to transfer a dCache file locally:

% gfal-copy srm://ccsrm.in2p3.fr:8443/pnfs/in2p3.fr/data/dteam/<my file> file:///scratch/<my file>