Castor: CERN Advanced STORage Manager

The CERN Advanced STORage manager (CASTOR) is a hierarchical storage (i.e. has disk and tape) management system which was developed at CERN for archiving physics data (with very large data volumes, see the plot on the right). Files can be stored, listed, retrieved and remotely accessed using CASTOR command-line tools or user applications that were developed using the CASTOR API. CASTOR provides a set of access protocols such as XROOT (the main and recommended protocol) and GridFTP. RFIO (Remote File IO) used to be supported until 2016.

CASTOR is the successor of SHIFT, the Scalable Heterogeneous Integrated FaciliTy for HEP computing, which was developed and operated in the 1990s. As of June 29th 2020, CTA, the CERN Tape Archive, started to be operated as the successor of CASTOR and gradually replaced it. The evolution of total data on tape at CERN since 2001 is displayed on the right, including statistics gathered from CASTOR 1 (1998-2007), CASTOR 2 (2005-2022), and CTA (2020-onwards).

Design

The design is based on a component architecture (Architecture diagram) using a central database in order to safeguard the state changes of the CASTOR components. The access to disk pools is controlled by the Stager; the directory structure is kept by the Name Server. The tape access (writes and recalls) is controlled by the Tape Infrastructure.

The 5 major functional modules are: