Anecdote: a few weeks ago, my father complained that after upgrading to macOS HighSierra, he was seeing rainbow beachball delays just using Microsoft Excel. These never happened before. I suspect APFS as the culprit. When file copying can be 100 times slower, you know that APFS is a science fair project.
The MacSales.com has some excellent tips for upgrading to macOS High Sierra without the forcible “upgrade” to APFS in Is It Possible Not to Convert to APFS When Upgrading to High Sierra?.
With either of these methods, install High Sierra on the same machine it is to be used on, because Apple rolls in firmware updates into the installer.
Safest way to upgrade to macOS High Sierra without APFS
The way that I strongly suggest doing this is the safest and easiest. Safest because if something goes awry, the upgrade can be dropped without changing what you already have:
- Clone the boot drive to any spare external drive.
- Boot off the spare/clone.
- Upgrade the spare/clone. The updater will leave the file system alone—it won’t be converted to APFS.
- Boot off the now updated spare/clone. Check things out and verify that things are working to your satisfaction—and don’t rush this. Make sure everything is acting right and that everything you normally do is OK as well.
- Satisfied? Clone the now updated external to the original boot drive.
- Boot from the original boot drive (now updated).
By doing it this way, there is no change to the existing boot drive until you explicitly choose to clone back over it with the updated system.
Upgrading to macOS High Sierra without APFS (less ideal)
This is less good, because if anything goes awry, you’ve been operating directly on the existing boot drive. The method above preserves that boot drive and lets you assess High Sierra first.
1. Let the High Sierra installer download, but when it launches, quit it. This will leave the installer in the /Applications directory.
Open a Terminal window
2. Paste in the following command, including the quotes:
"/Applications/Install macOS High Sierra.app/Contents/Resources/startosinstall" --converttoapfs NO