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Clean Install - Erase as APFS or Mac OS Extended?

iStorm

macrumors regular
Original poster
Sep 18, 2012
181
175
I'm planning on doing a clean install of Big Sur sometime after it is released. I was reading Apple's help articles to see what their documented steps were, but I'm confused on their first two bullet points about How to choose between APFS or Mac OS Extended.

How to choose between APFS and Mac OS Extended
Disk Utility tries to detect the type of storage and show the appropriate format in the Format menu. If it can't, it chooses Mac OS Extended, which works with all versions of macOS. If you want to change the format, answer these questions:
  • Are you formatting the disk that came built into your Mac?
    If the built-in disk came APFS-formatted, Disk Utility suggests APFS. Don't change it to Mac OS Extended.
  • Are you about to install macOS High Sierra or later for the first time on the disk?
    If you need to erase your disk before installing High Sierra or later for the first time on that disk, choose Mac OS Extended (Journaled). During installation, the macOS installer decides whether to automatically convert to APFS—without erasing your files.


I'm currently using Catalina and therefore have an APFS-formatted disk, so Disk Utility is going to suggest APFS when I erase it. The first bullet point says don't change it, but then the second one says to choose Mac OS Extended if installing High Sierra or later and it will be converted to APFS. These two points seem to contradict each other. Which one should it be (or the best one to choose)? Are there any benefits (or cons) in letting the installer do the conversion rather than using APFS right away?

The more I read the second bullet point, the more questions/thoughts run through my mind. Why does it say "High Sierra or later"? I know APFS was introduced with High Sierra, but earlier versions need to use Mac OS Extended too. Also, what does it mean by installing "for the first time on the disk"? Wouldn't macOS always be installed for the first time on an erased disk? I don't see why it would make any difference whether installing for the first time on a new disk vs. installing on an erased disk—they're both blank or empty. So why not keep that point simple and just say "Choose Mac OS Extended if you are installing macOS"? Now I'm back to my original/main question above...
 
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brianmowrey

macrumors 6502
Oct 5, 2020
363
105
Clearly that article just needs a rewrite.

Before Catalina that bullet was more elaborate, and we can grok that the purpose of the bullet is to keep users from doing a APFS High Sierra install on HDD:

Are you about to install macOS High Sierra or later on the disk?
If you need to erase your disk before installing High Sierra or later for the first time on that disk, choose Mac OS Extended (Journaled). During installation, the macOS installer decides whether to automatically convert to APFS—without erasing your files:

  • macOS Mojave: The installer converts from Mac OS Extended to APFS.
  • macOS High Sierra: The installer converts from Mac OS Extended to APFS only if the volume is on an SSD or other all-flash storage device. Fusion Drives and traditional hard disk drives (HDDs) aren't converted.

Now that we are into Catalina the context no longer makes sense; the title should say "If you are installing High Sierra on HDD." Even then, it doesn't really matter if you choose APFS, the Installer will switch it - as it did on my machine. The bullet still makes no sense because no one is going to "keep their files" while doing an erase regardless of format.

It's very straight-forward on the User Guide.
 
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