This message is issued when a the NUMSTREAM parameter is being specified with a value higher than the number of drives available to the device class.
The command continues.
The value will be updated as requested. If the number of drives available at the time the database backup is attempted is less than the number of streams, the database backup will be performed using the number of online drives as the number of streams. For example, if the number of available drives is 2 but the NUMSTREAM value had been set to 4, than the database backup will be done using only 2 streams.