This software uses this value for the buffer allocation size when you build the backup image.
When you back 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 BACKBUFSZ can help improve the performance of the Commvault backup utility as well as minimize the impact on the performance of other concurrent database operations.
If you want to have the DB2 software determine the buffer size, set the value to 0. If you do not set it to 0, the minimum value that you can enter is 8.
Use a buffer size that is a multiple of the extent size. If multiple table spaces have different extent sizes, the buffer size value must be a multiple of the largest extent size.