I am attaching a document that discusses various performance problems, and how to deal with them
Unfortunately, there is no simple answer for this problem. I agree, the performance you are seeing is incredibly bad. Ifyou are running file system backups, you can test by running Disk Agent (VBDA) in stand-alone mode to see if it is a problem with th emedia agent, then try backing up the same sample to a local 'nul' device to see if it is a network issue, then doing a nomral backup using the same sample. You need to be able to make an Apples-to-Apples conparison
You can try increasing your block size on your devie configuration. Make sure that, in the Destination tab of your backup specification, concurrency is set to '1'
Distributed File Media Format (DFMF) is only used in a very limited setting, and it usually causes more trouble that it si worth (for exampe, you can't delete media), and I recommend against using this option