Can I choose an installer on an external drive in Recovery mode?

[sfphoto]

Machine is 2014 Mini w/ Fusion Drive.
If one is to de-fuse the process requires installing an OS while still in Recovery mode.
Normally the original OS is downloaded from the Internet (OSX10.10 for a 2014 Mini).

Would be nice instead to choose an installer (newer) on an external drive.
Perhaps v10.10 Internet installation is mandatory though?

 

[Bigwaff]

I don't think Recovery is necessary if you have a macOS installer on USB media. Boot from the USB media and use Terminal to split the internal Fusion Drive using `diskutil` command. Disk Utility can't create or split Core Storage volumes. Then install macOS on which ever drive you prefer, most likely the HDD as Fusion Drive SSD are really small.

If you can download the macOS installer from internet, you can create install USB media. Plenty of tutorials on the web. Or you can download Mist app and let it create the USB install media for you.

GitHub - ninxsoft/Mist: A Mac utility that automatically downloads macOS Firmwares / Installers.

A Mac utility that automatically downloads macOS Firmwares / Installers. - ninxsoft/Mist

github.com

 

[sfphoto]

I don't think Recovery is necessary if you have a macOS installer on USB media. Boot from the USB media and use Terminal to split the internal Fusion Drive using `diskutil` command. Disk Utility can't create or split Core Storage volumes. Then install macOS on which ever drive you prefer, most likely the HDD as Fusion Drive SSD are really small.

If you can download the macOS installer from internet, you can create install USB media. Plenty of tutorials on the web. Or you can download Mist app and let it create the USB install media for you.

GitHub - ninxsoft/Mist: A Mac utility that automatically downloads macOS Firmwares / Installers.

A Mac utility that automatically downloads macOS Firmwares / Installers. - ninxsoft/Mist

github.com

Thanks!
I do have boot disks w/ installers for several OS versions. Will just need to determine the command syntax for the proper volume.
Was thinking to replace the PCIe card w/ a larger one. This seems much easier than removing the 'fused' HDD/PCIe and putting in an SSD, plus a PCIe would be faster.