When the storage maxes out, the Broker will go down with an error: Max Persistent storage reached, 0 k bytes remaining. Though you will see clients connected, no data flow could happen.
From the adapter_ping command you can check the status of adapters running on the broker- they will show as not-connected.
Future imports of integrations will fail because of this issue.
Further, storage should be either guaranteed or volatile, since going into ES 5.0, there is no concept of persistent storage.
Hope this helps.
#webMethods#Integration-Server-and-ESB