I want to emphasize, this is for testing purposes only
What I normally suggest for testing is to create a 'nul' file-type device located on the server where the backup is slow. Pick an Object to test with that will be consistent through the testing, that is, all tests will be of the same object or sub-object. Determine the size of what is being tested, and set FileMediumCapacity a little larger than this value
Create a backup specification for just this object. Enable the option "Display Statistical Info'
- Run the backup as you normally would, to an existing device. Save the session report
- Change the Destination to the 'nul' device, run the backup again. Save the session report
- On the server that you are testing with, run the VBDA in stand-alone mode (you'll probably need some help with this one). Save the session report.
Comparing the session reports may give you a clue as to what may be slowing down the backup