For example, network.target is pulled in by whatever service configures your network interfaces, therefore ordering your custom unit after it is sufficient since network.target is started anyway. The following figure shows how a typical Fibre Channel cluster configuration might look. Figure 1.1. Three-Server Cluster During normal cluster operation, each server is in constant communication with the other servers in the cluster and performs periodic polling of all registered resources to detect failure. Also please let us know as much information as possible about how and when the crash happens.