Online data backup services provide durable storage for user data without the hassle of traditional backup solutions, but comfort comes at a price. In this paper we focus on the costs of online data backup. First, we survey existing online backup pricing models: we compare unlimited and pro rata data plans, then we propose a novel, risk-based pricing scheme which suits risk-conscious users. Second, we build a simple Backup Selection Game where users can choose among these three cloud-based

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... ng schemes and the cost imposed by participating in a peerto-peer backup system. We show that rational users generally prefer the pro rata scheme, irrespective of the characteristics of individual users. On the other hand, heterogeneous equilibria may also emerge under certain distributions of data volume per user, due to the effect of buying storage in bulk. We also discuss how peer-to-peer backup could emerge under a more elaborate cost model.