Organizations are gradually outsourcing storage services such as online hosting files, backup, and archival to public providers. There are however concerns with this process because organizations cannot access files when the service provider is unavailable as well as they have no control and no assurance on the management procedures related to data. As a result, organizations are exploring alternatives to build their own multi-tenant storage capacities. This paper presents the design,

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... tion and performance evaluation of an approach for constructing private online storage services. A hierarchical multi-tier architecture has been proposed to concentrate these services in a unified storage system, which applies fault-tolerant and availability strategies to the files by passing redundant information among the services or tiers. Our approach automates the construction of such a unified system, the data allocation procedure and the recovery process to overcome site failures. The parameters involved in the performance of the storage services are concentrated into intuitive metrics based on utilization percentage, which simplifies the administration of the storage system. We show our performance assessments and the lessons learned from a case study in which a federated storage network has been built from four trusted organizations spanning two different continents.