bacula concurrently backup not working?

Question

I'm in strange situation.

Job is running concurrently but it's not taking time i expected.

It seem's like working nice.

(when i command status dir, both job's status is running)

Job1 tekes 4minutes and Job2 takes 5minute.

If i run two job at time, i was expect it takes 6~7minutes.

But Job1 finished first(it takes 4minute) and Job2 finished second.(it takes 5minute).

It takes 9minute like concurrent backup not working!

Two jobs have same prioryty, and this is config text i added for.

Is there any other option for concurrent backup?

Please help me T.T

bacula-dir.conf

set Director section's option Maximum Concurrent Jobs = 20

set Client section's option Maximum Concurrent Jobs = 20

set Storage section's option Maximum Concurrent Jobs = 20

set storage section's option Maximum Concurrent Jobs = 20

set Device secsion's option Maximum Concurrent Jobs = 20

set FileDaemon section's option Maximum Concurrent Jobs = 20

4 + 5 = 9 . Looks like you have a resource restriction, I'm going to guess I/O but it could be CPU. — Tim, Aug 07 '17 at 08:54
But when backup is running, I/O share is less then 20% and available memory is about 14GB. I can't understand why bacula dosen't use resource much. — ahreum hong, Aug 09 '17 at 05:17
Please edit your question to show information about I/O and CPU usage. If it's a spinning disk it could be that the hard disk is simply busy seeking. — Tim, Aug 09 '17 at 05:34