Traffic　fluctuations　make　conventional　multicast　tree　difficult　to　fully　utilize　the　residual　bandwidth　in　the　inter-datacenter　networks.　In　this　paper,　we　introduce　datacenter　storage　into　the　provisioning　process　of　multicast　transfers.　A　scheduling　method,　named　Store-and-Forward-Tree　(SnFTree),　is　proposed　for　multicast　transfers　in　the　software-defined　inter-datacenter　optical　network.　By　leveraging　temporary　storage　at　intermediate　sites,　a　multicast　tree　can　be　segmented　into　time-independent　subtrees　when　provisioning　an　entire　light-tree　fails.　Benefiting　from　the　broadcast　nature　of　optical　multicast,　intermediate　sites　can　provide　cut-through　routing　and　temporary　storage　simultaneously　with　negligible　processing　delay.　By　using　load-balancing　tree　computation,　traffic　can　be　balanced　across　the　network　efficiently.　Simulations　show　that　SnFTree　provides　extra　provisioning　flexibility　and　hence　outperforms　the　state-of-the-art　scheduling　methods　in　terms　of　blocking　probability　and　the　number　of　OpenFlow　Agent　updates.　©　2021　IEEE.