An IoT-oriented Multiple Data Replicas Placement Strategy in Hybrid Fog-Cloud Environment

The growing adoption of Fog computing for the sensitive-time IoT applications allows to facilitate the real-time actions and to enhance their efficiency and performance. In fact, keeping the data in the distributed Fog network brings the advantages and power of the Cloud closer to where data are generated while saving network bandwidth and reducing latency and operational costs. However, due to the diversity of the Fog nodes, IoT system distribution and data sharing, how and where to place the produced data with low latency is a main challenge. Moreover, a data placement based on a single replica cannot meet the data access requirements of all data consumers that have different topology positions. Thus, in this paper, we propose a multi-objective optimization data placement model in a hybrid Fog-Cloud environment based on multiple data replicas. It aims to find better distributed data storage while optimizing the overall system latency and the used storage space by minimizing the data replicas and following full and partial data replication methods. Further, we propose a greedy algorithm $iFogDP_h$ which uses a refined method to find a solution for assigning the IoT data to the appropriate data hosts in polynomial time by reducing the time required to transfer data for storage, access and replication. We conducted the experiments on iFogSim, a toolkit for modeling and simulation of Fog environments. The experimental results show the effectiveness of our proposed solution in terms of latency, storage overhead and the number of data replicas compared to the existing strategies.