Dell Precision T3600 Second HD Doesn't Appear In Windows 10

Need some help getting a second HD to appear in Windows 10 on my recently purchased (refurbished) Dell Precision T3600.

I did a clean installation of Windows 10 and ran all updates. 

The drive appears as SAS-3 on BIOS/System Configuration/Drives page.

However, the drive does not appear in Windows Device Manager or Windows itself.  

The second drive in question is cabled up to HDD3 on the MB. I tried HDD2; no change.

What am I missing?  What did I overlook?

Edit: SATA/RAID controller is now set to ENABLED.  No change, no second drive in Windows 10.

Thank you.