Analysis of the VAX/VMS error logs in multicomputer environments - A case study of software dependability

This paper presents an analysis of the software error logs produced by the VAX/VMS operating system from two VAXcluster multicomputer environments. Basic error characteristics are identified by statistical analysis. Correlations between software and hardware errors, and among software errors on different machines are investigated. Finally, reward analysis and reliability growth analysis are performed to evaluate software dependability. Results show that major software problems in the measured systems are from program flow control and I/O management. The network-related software is suspected to be a reliability bottleneck. It is shown that a multicomputer software Time Between Error distribution can be modeled by a 2-phase hyperexponential random variable: a lower error rate pattern which characterizes regular errors, and a higher error rate pattern which characterizes error bursts and concurrent errors on multiple machines. The VAX/VMS software reliability growth, during the measured period of more than three years and under the workloads running on the measured systems, can be modeled by a scaled exponential function which takes hardware-induced software failures into account.