Abstract
In this paper, a multistate cloud‐RAID (redundant array of independent disks) storage system subject to fault‐level coverage (FLC) is modeled and analyzed. Most of the existing works on reliability analysis of cloud‐RAID systems have either assumed binary‐state for storage disks or failed to consider imperfect fault coverage, an inherent behavior of fault‐tolerant systems. This work advances the state of the art by proposing a combinatorial method based on multivalued decision diagrams for analyzing reliability of a multistate cloud‐RAID system with FLC. The FLC is one common type of imperfect fault coverage behaviors, where the system fault recovery capability is dependent on the number of disk faults happening within a certain recovery window. Effects of the functional dependence behavior between the RAID controller and disks are addressed. The method is illustrated through a detailed analysis of an example cloud‐RAID 5 storage system. Numerical results are provided to show the impact of different design parameters on system performance. These results also demonstrate that failure to consider FLC leads to inaccurate system state probabilities, further misleading system design activities based on these probabilities such as maintenance and optimization.