To provide elastic cloud services with QoS guarantee, it is essential for cloud data centers to provision virtual machines rapidly according to user requests. Due to bandwidth bottleneck of centralized model, P2P model is recently adopted in data centers to relieve server workload by enabling sharing among VM instances. In this paper, we develop a simple theoretic model to analyze two typical P2P models for VM image distribution, namely, isolated-image P2P distribution model and cross-image P2P

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... distribution model. We compare their efficiency under different parameter settings and derive their corresponding optimal server bandwidth allocation strategies. In addition, we also propose a practical optimal server bandwidth provisioning algorithm for chunk-level crossimage P2P distribution mechanism to further improve its efficiency. Extensive simulations are conducted to validate the effectiveness of our proposed algorithm.