This parameter specifies the size of the buffer used when backing up the database if the buffer size is not explicitly specified when calling the backup utility. For more information about the backup utility, refer to the Command Reference.
When backing up a database, the data is first copied to an internal buffer. Data is then written from this buffer to the backup media when the buffer is full.
Tuning this buffer size can help improve the performance of the backup utility as well as minimize the impact on the performance of other concurrent database operations.