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.