6850 USB Problems

I have a 6850 running redhat 4 that is having usb drive issues. Note: I have 5 other 6850's setup like this, and this is the only one I have issues with. All my backups are copied to 160G USB drives Once a db copy begins(usually around 100G) it starts fast and then after 5 minutes completely stops. The box's cpu is running 100% at this point, and I need to reboot. Dell has replace the drives, cards, just about the whole server, they are stumped. I'm not an expert, but it seems like a cache issue. Can anyone help me out?