Local Storage at SLAC

For ATLAS users at SLAC there are various storage options which are aimed at different types of usage.

• AFS Home Directory
• NFS filesystems
• xrootd user space
• xrootd production space

AFS Home Directory

By default you get a fairly small AFS quota on your home directory. You can ask unix-admin to increase it to 500MB or for other volumes to be added to your home directory with a quota of 500MB. SCCS has a form to make this request.

NFS filesystems

Dedicated ATLAS scratch space is available. You should create a directory for yourself with the format: /afs/slac.stanford.edu/g/atlas/work/<firstLetterOfUsername>/<username>. It is actually an NFS disk space not backed up so that code are recommended to remain on your AFS space. For the moment this space is not automatically cleaned up, if it fills up we'll need to start doing that. Currently there are two 125GB volumes making up this space.

This space should be used for log files and other small files that don't need high performance access.

xrootd user space

This space is primarily for storing ROOT files, any type (event store and ntuples are two examples). xrootd offers high performance access to these types of files.

Access to this area is either directly from ROOT or by copying files in or out via xrdcp. The recommended access type is to use direct access for reading and to write via xrdcp (write the output to a local disk on the machine your job is on, this is /scratch on the batch workers with scratch space, or /usr/work on the interactive machines).

Files in xrootd have a URL-type format. You can add them to a job and Athena knows how to use them. An example file would be;

To access it in ROOT directly, do:

root[0] TXNetFile f("root://atl-xrdr//atlas/xrootd/usr/g/gowdy/myFile.root");

Filesystem type access is not transparent currently due to the distributed nature of the xrootd system. However, the xrootd filesystem is MOUNTED on atlint01. You can should make a directory called /"first letter"/"username"/ in /xrootd/atlas/usr.

xrootd production space

This are should be used for access to ATLAS datasets. You can use the instructions here to import datasets for your use.