Flexi-grid elastic optical network (EON) provides a promising infrastructure for datacenter (DC) interconnection with its flexible spectrum allocation and high-capacity transmission. Since failures in inter-datacenter elastic optical networks (IDC-EONs) will result in vast amounts of request interruptions and data loss, much recent research has focused on the survivability of IDC-EONs. In this paper, we investigate how to improve network survivability and provide 100% request protection under single-datacenter and single-link failures (single-DLFs) scenario by leveraging multiple DCs that can provide the same services. A shared backup path protection based on minimum spectrum occupancy combination strategy (SBPP-MSOCT) is proposed, which combines the existing spectrum occupancy of the network and select working and protection paths with the least spectrum consumption. Numerical results demonstrate that SBPP-MSOCT can effectively enhance network survivability while reducing spectrum resource consumption and request blocking probability compared to reference algorithms.