Install Mojave onto external SSD only?

[roadkill401]

I have had a very bad past experiences with my iMac and the OSX upgrade process. To be blunt, I am still somewhat in the camp of if it ain't broke then why go out and try and fix it? But I get that technology moves on and bug fixes security patches won't get applied to older versions of OSX.

Right now I have a working 2014 iMac 5K with a 512ssd inside. This is partitioned into two drives with Sierra 10.12 on one, and El Capitan 10.11 on the other as that was the last official version that Adobe CS6 supported and works for DreamWeaver that I use for my small business web page deployment and editing.

Now I have a ThunderBay 4 mini, with several SSD drives inside. I purchased a new 500gb SSD drive that I have a working copy of High Sierra loaded onto for Logic Pro and Final Cut. But it seems that Apple had decided that you need to have at least Mojave 10.14 for the latest releases of those programs. I'd like to be able to upgrade just the external SSD to the new OS and leave the internal drive on the iMac untouched.

Apple being the dicks they can be, will not say yay or nay as to if the upgrade will touch any other drive that is attached to the Mac from the HFS+ to APFS in the process of doing the upgrade. Or if the upgrade will only touch the drive/partition that the upgrade is being loaded onto. I can pull my Lacie drive so it is not connected. I can pull all my other drives out of the ThunderBay 4 so they can't get touched. I can do anything about the internal SSD drive inside the iMac that has my two main OS's installed on them. If they get converted to APSF then they won't boot and they will be effectively trashed. I'd prefer it if they were left alone.

Has anyone done and upgrade on and external drive, and does it touch any other attached storage in the upgrade process?

 

[casperes1996]

I did during the developer beta of Mojave, and have always done with betas, but not with the actual release. Though I am currently running Catalina externally with Mojave internally, though of course that’s a different circumstance. I can say though that the process shouldn’t touch anything but the drive it is pointed at, and it didn’t touch anything else during the beta at least

 

[roadkill401]

thank you for letting me know. I will give it a try. I have made a CC backup of the two internal partitions, so I guess there is a possible backout plan if I can figure out how to restore.

 

[Honza1]

I did this on prior macOS versions, but not Catalina. I would assume that installer modifies only drive on which it is installing... BUT, who knows?
So here is what I would do: Carbon Copy internal SSD(s) to USB drive, check it and store it safely away. Remove all other disks from the system I could. Install Catalina on external drive.
If installer modifies internal SSD, you can go back, use Disk tools to format to HSF+, partition and Carbon copy your old systems back.

 

[roadkill401]

Well, I am glad to report that it only touched the SSD drive attached to the Thunderbay 4, and left the internal iMac drives alone. The upgrade did take quite some time, in i think that it did more than just upgrade. When I downloaded the Mojave update, The system said it needed to install some patch first that took 45 minutes to install. I think that might have been some microcode from intel that I didn't get patched because I spend most of my time in 10.12 and that OS pre-dates the intel chip hacking/patch thing.

But all is well and seems to be working fine. If Mojave keeps working then I will consider moving full time over to it, and then I will just need to figure out how to make a bootable El-Capitan drive for my CS6-Dreamweaver .. or at some point figure out a different app to do that work. But then again, I own CS6 and it does work. why re-invent the wheel.

 

[Honza1]

You have another interesting option - run El-Cap in virtualization. You can run osx/macOS in virtual systems - I routinely run different versions of macOS (currently Catalina) on my main machine in Parallels VM. Works reasonably well and no need to reboot to different system when I need specific program on specific system. It is not speed daemon for sure, so if you need lots of power, that may not be the best option. It also costs money for license of virtualization software.
Personally, I disliked Dreamweaver, I am surprise you want to hold on it. I had to use it for ~10 years, and it was not a dream for sure. More like nightmare. I guess when you are used to it...

 

[casperes1996]

You have another interesting option - run El-Cap in virtualization. You can run osx/macOS in virtual systems - I routinely run different versions of macOS (currently Catalina) on my main machine in Parallels VM. Works reasonably well and no need to reboot to different system when I need specific program on specific system. It is not speed daemon for sure, so if you need lots of power, that may not be the best option. It also costs money for license of virtualization software.

VirtualBox is FOSS. Not as fast as Parallels, but free . So if speed really isn't a concern, there's that

 

[Fishrrman]

Mojave can be installed on an external drive, just like any previous version of the OS.
An SSD will work best for this.
USB3 SSD will do fine.