The cluster implementation used on the Hardware Appliance uses a regular network connectivity over the Application Interface for all cluster communication. This means that cluster nodes don’t have to be placed physically close to each other as long as they have good network connectivity.
However, this also means that a node cannot distinguish between the failure of another node and broken network connectivity to the other node. To avoid the situation where the cluster nodes operate independently and get diverging data sets (a so called split brain situation), the cluster nodes take a vote and will cease to operate unless they are part of the majority of connected nodes. This ensures that there is only one data set that is allowed to be updated at the time. In the case of a temporary network failure, disconnected nodes can easily synchronize their data to the majority’s data set and continue to operate.