An error was encountered and the unit is now operating in degraded (non-redundant) mode. This is usually due to a drive failure or the physical removal of a drive from a redundant unit.
Check hardware connections and reseat the drive or drives. Rescan the controller from 3DM 2 or CLI to see if the unit has been restored. If you are able to restore the unit before any data has been written to the unit, a rebuild will not be necessary. If the unit remains degraded, replace the missing or dead drives and initiate a rebuild.