Cloud　computing　promises　high　performance　and　cost-efficiency.　However,　most　cloud　infrastructures　operate　at　a　low　utilization,　which　greatly　adheres　cost　effectiveness.　Previous　works　focus　on　seeking　efficient　virtual　machine　(VM)　consolidation　strategies　to　increase　the　utilization　of　virtual　resources　in　production　environment,　but　overlook　the　under-utilization　of　backup　virtual　resources.　We　propose　a　heuristic　time　sharing　policy　of　backup　VMs　derived　from　the　restless　multi-armed　bandit　problem.　The　proposed　policy　achieves　increasing　backup　virtual　resources　utilization　and　providing　high　availability.　Both　the　results　in　simulation　and　prototype　system　experiments　show　that　the　traditional　1:1　backup　provision　can　be　extended　to　1:M　(M　＞＞　1)　between　the　backup　VMs　and　the　service　VMs,　and　the　utilization　of　backup　VMs　can　be　enhanced　significantly.