storage/ndb/src/kernel/blocks/backup/Backup.cpp:
  If FailedToSetupFsBuffers in BACKUP block, it will send back DEFINE_BACKUP_REF to LQH.
storage/ndb/src/kernel/blocks/dblqh/DblqhMain.cpp:
  If get DEFINE_BACKUP_REF signal , LQH will crash and give some messages in error log.