backup to disk write issues

Hello I'm new to netbackup after 5 years with HP Data Protector and I have some real concerns about write to disk performance.

It appears that we have queues waiting for the block to empty so we can write to disk.

we dont use SQL agents our DBA's want to do flat file backups which was a problem for HP and i was wondering if this could be the same issue where netbackup doesnt like millions of 10k files or 400gb + flatfile backups

could someone give me any idea where i should look to find out if this is the case 

Many Thanks in advance