MetaSync: File Synchronization Across Multiple Untrusted Storage Services.

Cloud-based file synchronization services, such as Drop-box, are a worldwide resource for many millions of users. However, individual services often have tight resource limits, suffer from temporary outages or even shutdowns, and sometimes silently corrupt or leak user data. We design, implement, and evaluate MetaSync, a secure and reliable file synchronization service that uses multiple cloud synchronization services as untrusted storage providers. To make MetaSync work correctly, we devise a novel variant of Paxos that provides efficient and consistent updates on top of the unmodified APIs exported by existing services. Our system automatically redistributes files upon reconfiguration of providers. Our evaluation shows that MetaSync provides low update latency and high update throughput while being more trustworthy and available. MetaSync outperforms its underlying cloud services by 1.2-10×on three realistic workloads.