Help needed with lg gh20ns10

I experience difficulties with my new LG burner. It runs on a asus A8v deluxe MB. It’s attached to the VIA SATA raid controller on the MB. When I burn a disc Nero detects 16*, but during the process the speed decreases to 2*. I have the latest firmware of the burner and also my drivers from the MB are up to date. Does anybody have a good advice for me?

Thank’s in advance,