Peer-to-peer (P2P) based video-on-demand (VoD) systems rely on the cooperation among peers to reduce the server workload. Recently, hard cache is used to further improve the system scalability, because the contents will not be immediately cleaned up when the users get offline. However, how many practical benefits hard cache will bring to the P2P based VoD service has not been well studied and still remains far from clear. In this paper, we first characterize user behavior model with the benefit of millions of real VoD traces and identify several practical factors which potentially impact the system performance. Then we further conduct extensive trace-driven simulations to evaluate the scalability of P2P based VoD system with hard cache enabled and some interesting results are found.
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