I have always found that iperf far exceeds the performance with NetBackup, even when as you suggest trying to use similar buffer sizes.
I think you may be better off testing with NetBackup. You can use the GEN_DATA directives to create data without involving disk read speeds:
http://www.symantec.com/docs/TECH75213
you can then create a disk storage unit on the Media Server for your test policy and use the SKIP_DISK_WRITES touch file:
http://www.symantec.com/docs/TECH69948
(Beware as that will disable it for all disk backups!)
I have not myself tried this yet….but in theory it will just test the data transfer between the client and media server.
William D L Brown
Wonder what iperf settings best simulates netbackup, in regards to window size & parallel streams
Thinking that the windows should be the same as NET_BUFFER_SZ & parallel same as active jobs