Scratch Areas in DELPHI

There are two logical scratch areas under AFS for DELPHI users, and there are also two others which are not under AFS, thus not as easily accessible (specially for writing). All of them are not backed-up. The ones on AFS are accessible through the environment variables $AFS_SCRATCH (or just $SCRATCH) and $SCRATCH_WEEK; as the name suggests, the latter is intended for files that would need a longer lifetime, even if this cannot be guaranteed.

The $SCRATCH disk is intended to store typical short-lived files, of the few MB size, needed for just a few days. Obvious examples are the compilation results, intermediate files etc - whatever takes a lot of space while can be easily recreated. The file lifetime decreases quickly for big files or for users who exceed 200 MB in total.

The $SCRATCH_WEEK is for everyday-use files of size below 50-100 MB. Typical examples are postscript files, figures etc, needed when working on a publication. Again the file lifetime decreases quickly for big files or for users who exceed 256 MB in total.

Please note that Ntuples and DST-extracts should not be kept on AFS, because the access to such files is extremely slow, due to AFS cash mechanism and inefficient connection to PLUS machines. For those purposes exist non-AFS scratch areas - see below.

Please note also that AFS is rather fragile - by putting very big or very many files on it, one can easily crash the server (and then the whole volume becomes inaccessible). Therefore avoid un-archiving there big files with external packages - the /tmp area is much better suited for that (and on LXPLUS it is much bigger!).

Since the scratch areas tend to become full, a garbage collector is run to do some clean-up. A presentation (PS.gz,72KB) of the algorithm used was given at a Software Forum on 5 December 1996. The garbage collector daily produces a log file for each scratch area, with the list of files that have been deleted. The log files produced in the last week are available.

For big files needed just for a few days, a $CASTOR_SCRATCH area can be used. It is not under our garbage collector control, so the lifetime of files is not very well defined (it depends on the overall DELPHI Castor usage), but normally a few days is not a problem - sufficient, e.g. to transfer the file to your home lab. And of course if the file is needed for longer, then it should be stored directly in the user's $CASTOR_HOME directory. Please see our page with hints on the Castor usage.


Questions, comments, remarks to delphi-core@cern.ch
Created by Francesco Giacomini
Last modified: 6 Nov 2003 R.Gokieli