Recording to a second drive with fraps

Everywhere I've seen that you should record fraps videos to a second drive to reduce lag. I was running out of space on my hard drive so I went out and bought a 1.5T external hard drive. Whenever I try to record anything theres SOOOOOOO MUCH LAG. The framerate just absolutley plunges down to about 10-20. Its terrible. Is there something I can do to fix this? Are there any settings I need to change?

If you're using it with usb,that's the problem.MonsieurX

^^ This poster is correct. USB is much slower than internal SATA.