Accessing data from the Grid - comrademarvin/SA-ALICE-O2 GitHub Wiki

Most Run 3 data (and converted Run 2 data) that is used as input to O2 (in the format of AO2D root files) will be accessed from the Grid. There are exceptions, such as the case of locally running simulations that will output the AO2D locally. There is more than one way to access data from the Grid, the main approaches are:

  1. Download from MonALISA

Data files can be downloaded directly from the browser via MonALISA, by simply navigating to the file path of the required file and clicking on it to download. All simulation and experimental data can be accessed this way.

NB: This is only recommended for small enough files - only on the order of MBs. Otherwise the file download might hang for a long time and take very long to finish, or even just fail.

  1. Download via JAliEn

Data files can also be downloaded locally from the Grid using JAliEn (xjalienfs is a package that forms part of O2) - which can simply be done via the alien_cp command. Using the JAliEn cache manager approach is also described in Downloading AO2D from the Grid.

This method is recommended for larger data files that need to be downloaded locally.

  1. O2 Physics

When running an O2 Physics analysis task, it is also possible to merely specify the path of the file on the Grid as input - without having to download the file locally. The O2 software will then smartly locate the nearest storage location of the file and access it directly. This is especially useful when running Grid jobs. More details can be found at Running O2 Physics.