Unlike RBDs, which are simply a concatenation of objects, CephFS requires consistent data in both the data and metadata pools. It also requires a healthy CephFS journal; if any of these data sources have issues, CephFS will go offline and may not recover. This section of the chapter will look at recovering CephFS to an active state and then further recovery steps in the scenario that the metadata pool is corrupt or incomplete.
There are a number of conditions where CephFS may go offline but will not result in any permanent data loss; these are often caused by transient events in the Ceph cluster but shouldn't result in any long-term data loss, and in most cases CephFS should automatically recover.
As CephFS sits on RADOS, barring any software bugs in CephFS, any data loss or corruption should only occur in the instance where there has been a data loss occurrence...