*6.10.2 Distributed*

Cloud System Architecture: In [26] the authors present a cloud architecture that provides high dependability of the system based on severe redundancy. The architecture is composed of multiple datacenters that are geographically separated from each other. Each datacenter includes VMs are active in physical. To perform DR, there is a backup server that stores a copy of each VM. In the case of a disaster, which makes a datacenter unavailable, the backup site transmits VM copies to another datacenter. Although this system architecture is expensive, it highly increases the dependability which can be adequate for (IaaS clouds. In addition, the aforementioned paper describes a hierarchical approach to model cloud systems based on dependability metrics as well as disaster occurrence using the Statistic Petri Net approach.
