Migrating a clusteredIBM® WebSphere® Portal Express® environment occurs on a per cluster basis rather than a per node basis. To achieve high availability migration, your portal site must have a multiple cluster topology already in place. Replicated clusters must be in separate cells. You can also choose to migrate your environment with coexistence, which allows you to migrate your clustered source environment while keeping in production until the migration is complete. This migration scenario allows systems to keep running with less disruption and downtime to the users accessing WebSphere Portal Express. You can also migrate with coexistence when you do not have a multiple cluster environment.