Both economic reasons and interoperation requirements necessitate the deployment of IaaS-clouds based on a share-nothing architecture. Here, live VM migration becomes a major impediment to achieving cloud-wide load balancing via selective and timely VM-migrations. Our approach is based on copying virtual disk images and keeping them synchronized during the VM migration operation. In this way, we ameliorate the limitations set by shared storage cloud designs as we place no constraints on the cloud's scalability and load-balancing capabilities. We propose a special-purpose file system, termed MigrateFS, that performs virtual disk replication within specified time-constraints while avoiding internal network congestion. Management of resource consumption during VM migration is supervised by a low-overhead and scalable distributed network of brokers. We show that our approach can reduce up to 24% the stress of already saturated physical network links during load balancing operations.