Galera, MariaDB and multiple datacenter

Looking into using Galera and MariaDB across 3 data centers. We have a metroE comnection between the sites. Connectivity is pretty stable, but my concern is if a WAN link goes down at one of the sites, and I am writing to the local nodes. How does it handle that situation? How many nodes at minimum at each site is recommended? This question was similar, but different: https://stackoverflow.com/questions/27777134/galera-cluster-replication-between-two-data-centers/27793927#27793927