Why doesn't my Mac Pro see my new 4TB SATA drive? I purchased a Seagate ST4000DX001 4TB SATA Hybrid Drive (SSHD) and installed it into my Mac Pro (six core 3.33 GHZ MacPro5,1) in one of the internal SATA drive bays. However, the system didn't see it at all. Disk Utility didn't show the drive for me to format and the SATA Devices section under Apple System Profiler didn't show the drive listed at all.

The drive works because if I put it into a USB3 enclosure then it works, but since the Mac pro only has USB2 it's pointless for me to use it in a USB3 enclosure.

Why doesn't my Mac Pro see my Seagate 4TB SATA SSHD drive?
You've done all that I usually do to troubleshoot this in that you already know to use System Profiler to check the SATA bus for devices.

I would reboot the system and reset the NVRAM twice (keep holding the keys down and you'll hear the chime twice) and then re-check the profiler.

Sadly, if the controller doesn't make that device available - you'll need to use it connected to a non-optimal bus while you work with Seagate and/or Apple tech support to determine at a device driver level what settings need to be tweaked or updated to expose that particular drive to your Mac. Let's hope someone has the same drive and can either confirm or deny for their OS X level that the drive works for them.