Virtual machine migration is a useful and widely used workload management technique. However, the overhead of moving gigabytes of data across machines, racks, or even data centers limits its applicability. According to a recent study by IBM, the number of distinct servers visited by a migrating VM is small; often just two. By storing a checkpoint on each server, a subsequent incoming migration of the same VM must transfer less data over the network. Our analysis shows that for short migration intervals of 2 hours on average 50% to 70% of the checkpoint can be reused. For longer migration intervals of up to 24 hours still between 20% to 50% can be reused. In addition, we compared different methods to reduce the migration traffic. We find that content-based redundancy elimination consistently achieves better results than relying on dirty page tracking alone. Sometimes the difference is only a few percent, but can reach up to 50% and more. Our empirical measurements with a QEMU-based prototype confirm the reduction in migration traffic and time.