DL380e Gen8 - Can't use all 8 drive bays

Hi everyone,

I have an 8-bay DL380e Gen8 with the P420 RAID Controller.

I added 3 new HDD's to try and create a RAID-5, but one of the drives isn't recognized.

Bays 1-4 are used without problems, but any additional bay isn't spinning up the drive, and I know it isn't a problem with the drive itself.

The backplane was originally connected to the internal B120i controller, but I connected a single cable to the P420, which does have two ports.

Does the 2nd port on the P420 need to be connected to the backplane, or is there something else that I'm missing? 

Thanks for any help :)