File storage management for TFTR physics data

The desire to maintain ready access to data files covering the entire history of Tokamak Fusion Test Reactor (TFTR) has created a need for more economical methods of mass storage. This need was addressed through a combined hardware and software approach. This involved the purchase of a SONY optical disk subsystem with an auto changer (the `Jukebox´) which provides 160 Gbytes of online storage. The software constitutes a transparent layer integrating the Jukebox into the existing data file access methods. The system caches files on magnetic disks, which are managed automatically, so that they never exceed capacity. Newly created files are copied to the Jukebox for long-term storage and to magnetic tapes for backup purposes. The data remain on magnetic disks until a need for more space causes them to be skimmed according to frequency of use. Users can access any skimmed file just as though it were still on the magnetic cache. The system restores the file transparently within seconds, without need for manual intervention