A Migration Zone acts as boundary around a set of compute nodes. It provides a way to organize a collection of resources virtually and consists of a defined set of compute nodes (with any categories/tags) and connectivity to one or more storage pools. One compute node can belong to one migration zone.
Application instances can migrate among nodes within a migration zone, but cannot migrate to nodes outside of a migration zone. Migrating an instance from one compute node to another within a migration zone is equivalent to VMware's vMotion: there is zero downtime, continuous service availability and complete transaction integrity. When an instance starts in a particular migration zone, it will only utilize the compute nodes in that zone.
For a migration zone to support application instances, it must be connected to at least one storage pool. The resources in a migration zone must also be allocated to at least one virtual datacenter before they can be used to run application instances.