et al:
So I looked over the choices of HD suggested by MB and compared a few choices on the OWC suggested list, and within the few options that were in that $49.99 range the features were fairly comparable, but the Staples choice I found only had 32MB cache v 64 for the Barracuda, and then it appears that the Barracuda uses way less electricity when "idle" . . . so I went with the suggestion from MB and pulled the trigger . . . "free shipping" puts it several days away.
In the meanwhile, a couple of questions come to mind, if I want the "newer, fresher, faster" HD to be the default boot option, still planning on doing the multi-boot set up, etc . . . do I need to put that drive in the number one slot, where I assume the "older" HD is now residing? Moving the existing drive from one to let's say two, and then using OSX DU from #2 to format the drive into pieces of itself??
Or, do I need to keep the old drive in number one slot . . . format the new drive . . . and then either move them to new for number one, and older for number two?
I haven't done the multiple drives in one computer before, and then I have the mix of various OSX installs, with the GRUB booted choices of various versions of OpenSUSE . . . and then a new HD . . . with variations of the same thing, might keep it more simple, the **new** OSX 10.13 High Sierra formatted as HFS+ up front, and then later in the HD a Tumbleweed . . . with something I haven't tried, a Geckolinux MATE "rolling" edition . . . based on TW, sort of like Ubuntu is to Debian I believe.
Right now if I want OSX options I use the alt key on boot, and if I want OpenSUSE I just boot and the GRUB window opens and gives me the list of choices . . . so TW is the "default" boot if I just hit the power button and stand back . . . . I'm imagining it might be a tad "different" with two HD's?? Or mobo "sees all, tells all" . . . no worries, mate; they all get added into the list in a fluid fashion??
