Service　function　chains　(SFC)　mapping　takes　the　responsibility　for　managing　virtual　network　functions　(VNFs).　In　SFC　mapping,　existing　solutions　duplicate　VNFs　with　redundant　instances　to　provide　high　availability　in　response　to　failures.　However,　as　a　compromise,　these　solutions　result　in　high　resource　consumption　due　to　device　maintenance.　In　this　paper,　we　propose　a　novel　method　named　dynamic　backup　sharing　(DBS)　that　allows　SFCs　to　dynamically　share　backups　to　reduce　resource　consumption.　DBS　formulates　the　problem　of　sharing　backups　among　different　VNFs　as　an　integer　linear　programming　(ILP).　Thereafter,　we　design　a　novel　online　algorithm　based　on　dynamic　programming　to　solve　the　problem.　The　experimental　results　indicate　that　DBS　outperforms　state-of-the-art　works　by　reducing　resource　consumption　and　improving　the　number　of　accepted　requests.