[ML110 ProLiant G7]

I am trying to get this to boot but I don't know what I am doing wrong. I am new to servers and this server won't recognize my Unraid usb as a bootable drive. Any idea what I would need to change. 

[I just got a Hp Proliant ML110 G7]

I have selected the usb Driveway option as the IPL:1 in the bios then when I boot I get and error saying no bootable drive, insert floppy disk. I try then tried to use the f11 advanced boot and select usb drive and I get the same message. im pretty new to this and I am kinds lost.

[Can I use an external hard drive via usb]

I am using a 4-1Tb drive array and I have an external 2tb drive that has usb. First of all will I be able to add it to the array like usual? Secondly giving its 2tb and the rest of my drives are 1 tb, would it become the parity drive? Also I think I posted this in the wrong sub form