I have a hard drive enclosure with 2 sata hard drives but computer doesn't recognize it's connected?

I have an OWC Mercury Elite Al-Pro Enclosure with 2 Apple 1TB SATA drives in it, But my Mac Pro running Mavericks doesn't recognize the unit is attached. I thought it would show up under disk utilities and I could configure from there. But I can't do anything because the computer doesn't see it? Can anyone tell me what I'm doing wrong?