MetaSync: File Synchronization Across Multiple Untrusted Storage Services

Cloud-based file synchronization services, such as Drop-box and OneDrive, are a worldwide resource for many millions of users. However, individual services often have tight resource limits, varying performance in re-gions of the world, temporary outages or even shut-downs, and sometimes silently corrupt or leak user data. We design, implement, and evaluate MetaSync, a se-cure 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 lineariz-able updates on top of the unmodified APIs exported by existing services. Our system automatically redistributes files upon adding, removing, or resizing a provider with a novel deterministic replication scheme. Our evaluation shows MetaSync provides low update latency and high update throughput, close to the perfor-mance of commercial services, but is more reliable and available. For synchronization, MetaSync outperforms its underlying cloud services by 1.2X-10X on three real-istic workloads.