Abstract
Existing works on reliability modeling of cloud systems have assumed perfect fault detection and recovery mechanisms. In this paper, we relax this assumption by presenting combinatorial approaches based on binary decision diagrams for reliability analysis of a cloud-RAID 5 system subject to imperfect fault coverage. Both element level coverage and fault level coverage are addressed. Numerical example results are provided to illustrate effects of those two types of imperfect fault coverage on the reliability performance of cloud storage systems.