To be able to recover from a disaster, you first have to understand and be able to recognize one. For the purpose of this chapter, we will work with the assumption that anything that leads to a sustained period of downtime is classed as a disaster. This will not cover scenarios where a failure happens that Ceph is actively working to recover from, or where it is believed that the cause is likely to be short lived. The other type of disaster is one that leads to a permanent loss of data unless recovery of the Ceph cluster is possible. Data loss is probably the most serious issue as the data may be irreplaceable or can cause serious harm to the future of the business.