  We present a hierarchical simulation approach for the dependability analysis
and evaluation of a highly available commercial cache-based RAID storage
system. The archi-tecture is complex and includes several layers of
overlap-ping error detection and recovery mechanisms. Three ab-straction levels
have been developed to model the cache architecture, cache operations, and
error detection and recovery mechanism. The impact of faults and errors
oc-curring 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 devel-oped using DEPEND, a simulation-based environment for
system-level dependability analysis, which provides facili-ties 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 parame-ters characterizing fault injection in a given
submodel cor-respond to probabilities evaluated from the simulation of the
lower-level submodel. Based on the proposed method-ology, we evaluate and
analyze 1) the system behavior un-der 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 distribu-tions, and 3) the
accumulation of errors in the cache and in the disks.
