A hierarchical approach for dependability analysis of a commercial cache-based RAID storage architecture

We present a hierarchical simulation approach for the dependability analysis and evaluation of a highly available commercial cache-based RAID storage system. The architecture is complex and includes several layers of overlapping error detection and recovery mechanisms. Three abstraction levels have been developed to model the cache architecture, cache operations, and error detection and recovery mechanism. The impact of faults and errors occurring in the cache and in the disks is analyzed at each level of the hierarchy. A simulation submodel is associated with each abstraction level. The models have been developed using DEPEND, a simulation-based environment for system-level dependability analysis, which provides facilities to inject faults into a functional behavior model, to simulate error detection and recovery mechanisms, and to evaluate quantitative measures. Several fault models are defined for each submodel to simulate cache component failures, disk failures, transmission errors, and data errors in the cache memory and in the disks. Some of the parameters characterizing fault injection in a given submodel correspond to probabilities evaluated from the simulation of the lower-level submodel. Based on the proposed methodology, we evaluate and analyze 1) the system behavior under a real workload and high error rate (focusing on error bursts), 2) the coverage of the error detection mechanisms implemented in the system and the error latency distributions, and 3) the accumulation of errors in the cache and in the disks.