Storage Tradeoffs in a Collaborative Backup Service for Mobile Devices

Mobile devices are increasingly relied on but are used in contexts that put them at risk of physical damage, loss or theft. We consider a fault-tolerance approach that exploits spontaneous interactions to implement a collaborative backup service. We define the constraints implied by the mobile environment, analyze how they translate into the storage layer of such a backup system and examine various design options. The paper concludes with a presentation of our prototype implementation of the storage layer, an evaluation of the impact of several compression methods, and directions for future work

1. Introduction

Embedded computers are becoming widely available, in various portable devices such as PDAs, digital cameras, music players and laptops. Most of these devices are now able to communicate using wireless network technologies such as IEEE 802.11, Bluetooth, or Zigbee. Users use such devices to capture more and more data and are becoming increasingly dependent on them. Backing up the data stored on these devices is often done in an hoc fashion: each protocol and/or application has its own synchronization facilities that can be used when a sister device, usually a desktop computer, is reachable. However, newly created data may be held on the mobile device for a long time before it can be copied. This may be a serious issue since the contexts in which mobile devices are used increase the risks of them being lost, stolen or broken.