Persistence

The Event Hub secures event data and event data delivery by persistence. Incoming event data is persisted as well as outgoing event status, that is, if the event has been sent to a subscriber. When an event has been sent to all subscribers, it is removed from the persistence. If a subscriber is busy, the events will be persisted by the Event Hub until they can be processed.

Note: 

The events should only be persisted for a limited time. The Event Hub is not an archive.