Data Guard 12c: Warning: standby redo logs not configured for thread 1, Insufficient SRLs

Well, I have configured some 30 ‘Data Guards’ by now, but I never came across this warning, it seems it’s new in 12c:

DGMGRL> validate database cdb1dgsara

  Database Role:     Physical standby database
  Primary Database:  cdb1dgkara

  Ready for Switchover:  Yes
  Ready for Failover:    Yes (Primary Running)

  Future Log File Groups Configuration:
    Thread #  Online Redo Log Groups  Standby Redo Log Groups Status
              (cdb1dgkara)            (cdb1dgsara)
    1         3                       2                       Insufficient SRLs
    Warning: standby redo logs not configured for thread 1 on cdb1dgsara

Hang on, standby redo logs not configured? I have 4 groups! Continue reading