The use of a VAX cluster for the DIII-D data acquisition system

The DIII-D tokamak is a large fusion energy research experiment funded by the Department of Energy. The experiment currently collects nearly 40 Mbytes of data from each shot of the experiment. In the past, most of this data was acquired through the MODCOMP Classic data acquisition computers and then transferred to a DEC VAX computer system for permanent archiving and storage. A much smaller amount of data was acquired from a few MicroVAX based data acquisition systems. In the last two years, MicroVAX based systems have become the standard means for adding new diagnostic data and account for half the total data. There are now 17 VAX systems of various types at the DIII-D facility. As more diagnostics and data are added, it takes increasing of time to merge the data into the central shot file. The system management of so many systems has become increasingly time consuming as well. To improve the efficiency of the overall data acquisition system, a mixed interconnect VAX cluster has been formed consisting of 16 VAX computers. In the cluster, the software protocol for passing data around the cluster is much more efficient than using DECnet. The cluster has also greatly simplified the procedure of backing up disks. Another big improvement is the use of a VAX console system which ties all the console ports of the computers into one central computer system which then manages the entire cluster