This paper presents the design and implementation of a peer-to-peer storage system that allows mobile users to transparently access and share data. The system employs a small networked portable storage device that is designed to compensate for weak wide-area connectivity by leveraging ad hoc peer-to-peer connectivity and an embedded storage element. Other key features of the system include the use of a location and topology- sensitive multicast-like solution for locating data, lazy peer-to-peer propagation of invalidation information for ensuring consistency across multiple devices, and a distributed snapshot mechanism for supporting sharing and distributed backup. A common theme of the design decisions is minimizing the amount of distributed state and global coordination, while still achieving the desired functionality and good performance. Initial experiences with a prototype implementation suggest that we have largely achieved our objectives.