(ttt)-mmmmm(yy), THE
BACKUP-WHILE-OPEN STATUS FOR DATA SET dsname IN CATALOG
catalog_name ON VOLUME volume_serial_number IS BEING CHANGED
FROM nnn1 TO nnn2
Explanation
The current Backup-While-Open (BWO) status is changed to nnn before the data set is dumped.
See MSGADR720I for an explanation of the BWO status meanings.