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The Farsite distributed file system provides availability by replicating each file onto multiple desktop computers. Since this replication consumes significant storage space, it is important to reclaim used space where possible. Measurement of over 500 desktop file systems shows that nearly half of all consumed space is occupied by duplicate files. We present a mechanism to reclaim space from this incidental duplication to make it available for controlled file replication. Our mechanism includes 1) convergent encryption, which enables duplicate files to coalesced into the space of a single file, even if the files are encrypted with different users' keys, and 2) SALAD, a Self-Arranging, Lossy, Associative Database for aggregating file content and location information in a decentralized, scalable, fault-tolerant manner. Large-scale simulation experiments show that the duplicate-file coalescing system is scalable, highly effective, and fault-tolerant.

The tremendous popularity of wireless systems in recent years has led to the commoditization of RF transceivers (radios) whose prices have fallen dramatically. The lower cost allows us to consider using two or more radios in the same device. Given this, we argue that wireless systems that use multiple radios in a collaborative manner dramatically improve system performance and functionality over the traditional single radio wireless systems that are popular today. In this context, we revisit some standard problems in wireless networking, including energy management, capacity enhancement, mobility management, channel failure recovery, and last-hop packet scheduling. We show that a systems approach can alleviate many of the performance and robustness issues prevalent in current wireless LAN systems. We explore the implications of the multi-radio approach on software and hardware design, as well as on algorithmic and protocol research issues. We identify three key design guidelines for constructing multi-radio systems and present results from two systems that we have built. Our experience supports our position that a multi-radio platform offers significant benefits for wireless systems. 1

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