The CERN Advanced STORage manager (CASTOR) is a hierarchical storage management system which was developed at CERN for managing physics data files. Files can be stored, listed, retrieved and remotely accessed using CASTOR command-line tools or user applications using the CASTOR API.
CASTOR files are always accessed via disk. These files that are transparently saved to and recalled from tape. CASTOR provides a set of access protocols such as XROOT, GridFTP. and RFIO (Remote File IO).