The official HPSS introduction pages at CERN offer a more complete description of HPSS.
Here I will just summarise the absolute basics for getting to the data.
The High Performance Storage System is a "Hierarchical Storage Management System in which data are stored in classes of storage (disks and tapes), automatically managed by the store software." The user sees a directory structure - similar to AFS - hiding the tape number and sector etc.
The DSTs from the 2000 beam test are stored HPSS under /hpss/cern.ch/atlas/testbeam/sct/2000/dst with names dst[run number].root
A number of tools is available in /afs/cern.ch/project/hpss/public/ to inspect directories and store and retrieve data:
For the last two operations are only permitted to a limited amount of users. The first three should be possible from all machines in the ATLAS cluster. As an example, typing /afs/cern.ch/project/hpss/public/hpssget /hpss/cern.ch/atlas/testbeam/sct/2000/dst/dst2400.root mydst.root results in a download of the DST of run 2400 into the CWD with name mydst.root.
Each DST is around 1 to 20 MB, depending on the number of modules and the threshold.
Last update July 12, 2000