Formatting 2nd hdd to be viewed as 1 location in finder

You’ll need to review your drives within Disk Utility to figure things out.

Lets be clear here, you have two discreet drives which should show up in Disk Utility as well as on your desktop as Drive-A and Drive-B.

If you don’t then you either setup the drives into a Fusion Drive set which is not something I would do! In that case you’ll see the one drive Drive-A(b) were b is hidden! As it’s acting as a cache drive to the primary drive.

Now you’re not going to like this! I don’t recommend using APFS file systems on older SATA based systems. Unlike the older HFS+ file system APFS is very chatty!

While on the surface this doesn’t seem like a big deal it is! Think of it this way your Aunt is a big talker on the phone telling you just about everything without taking a breath! You just can’t get a word in! Before you know it the subject has changes over eight or ten times so responding to the first or second subject at this point is pointless!

This domination of the phone line clearly messes with your need to tell your Aunt something important. This is what happens within the a heavy dialog point as SATA connections are limited in there buffers unlike PCIe which is much deeper!

So, we need to stick with a macOS which is HFS+ based, that only leaves Sierra (10.12.x) on SATA systems.

Just because Apple supports your older system with the newer OS’s its not always wise to do it!