I have late 2012 iMac 27" (core i7, 32GB Ram, 2GB Graphics) that has a Fusion drive AND an external drive box that doesn't support conversion to APFS. Can I upgrade to Mojave and use HFS+ file system or do I have to wait until I nix the Fusion drive AND/Or upgrade the external HD box??
The answer is yes, that iMac can be upgraded to Mojave. The installer will perform APFS conversion for volumes on which it is installed. The installer will not attempt to alter the Time Machine backup drive's file format nor should you attempt to either.
Mojave will run on a drive formatted as HFS+, but it will not be able to install updates via the Software Update preference in System Preferences, and the standalone OS and Security Updates via the Apple Support Downloads page will only install on APFS formatted drives, unless you alter the Distribution file in the install.pkg.
As dialabrain stated, Fusion drives are fully supported, and as for the external, there is no reason to convert it to APFS and Mojave won't even try.
So, Can I upgrade to Mojave and retain HFS+ file systems for now?
Not on your startup drive. Not sure why you'd want to.
Time Machine drives must be HFS+. It doesn't work with an APFS destination.
The format of the drive being backed up doesn't matter.
You seem to be thinking there is a problem where there isn't one.
Fusion drives are supported by Mojave. No idea why you think your external isn't.
In disk utility click on the drive then Edit and Apfs conversion is grayed out. I know Fusion drives are supported but do they have to be converted to APFS ?? And, The external drive is my Time Machine drive. So, Can I upgrade to Mojave and retain HFS+ file systems for now?
I'd only want to retain HFS+ if I needed to for compatibility. Sounds like I'm upgrading. Thank you all for your assistance.
Upgrading from High Sierra to Mojave but retaining HFS+ file systems
