The inquiry about the performance issue did not include nearly enough to formulate any kind of accurate answer, so, we would need to know some basic things
First, are you backing up to Disk or Tape? The most common cause for performance issue when backing up to tape is not keeping the tape drive streaming. If the tape drive is constantly stopping and starting, this can cause a performance hit of up to 90%. As Andre implied, the way to avoid this is by increasing the concurrency in the backup specification so that more data streams are flowing to the device. The default is 4, but most modern tape drives easily can handle a concurrency of 10 or 12. I am attaching a PowerPoint presentation that describes this phenomenon
If backing up to a Virtual Tape Library on a Disk, a Concurrency of 1 shoud be used, and add as many Virtual Drives as you have licenses for
If this affects an Applications Backup, this approach won't help much, these are usually backed up with a Concurrency of 1 or 2 at the most (SAP allows multiple data streams)
I am also attaching a document that talks about performance issues in general, and some of the things that you can do to help with this
