From osxdaily.com
MacOS High Sierra includes the all new APFS file system, which is arguably one of the most significant new features introduced in the new Mac operating system update. Nonetheless it’s possible that some Mac owners with SSD volumes will want to not convert the existing HFS+ file system to APFS file system when installing macOS High Sierra. With a little command line magic, you can skip converting to APFS during the macOS High Sierra installation process if desired.
How to Install macOS High Sierra Without Converting to APFS File System
This is not recommended and should only be applicable to advanced users who have specific reasons to not want to convert a Mac to APFS. APFS is faster and offers better encryption, amongst other benefits, so it’s generally recommended to use APFS if the Mac supports it. APFS is currently only supported on SSD drives, with Fusion drives support for APFS soon to arrive in a future Mac software update.
How to Not Convert to APFS During macOS High Sierra Installation
By skipping APFS conversion of file system, macOS High Sierra will install with the longstanding HFS+ file system instead.
1. Download the MacOS High Sierra installer from the App Store as usual, making sure it’s within the /Applications/ directory*
2. Open the Terminal application, found in /Applications/Utilities/ (or from the Utilities screen menu options if booted from a USB boot installer)
3. Enter the following command syntax at the command line prompt:
/Applications/Install\ macOS\ High\ Sierra.app/Contents/Resources/startosinstall --converttoapfs NO
4. Hit return key to start the macOS High Sierra install process with the –converttoapfs NO directive, thereby skipping the APFS conversion of existing file system
* You will need the full installer to have the Contents/Resources/ options available to you. You can download the full macOS High Sierra installer with these instructions if you’re getting the little mini-installer without /Content/Resorouces/ folder.
In case you were wondering, skipping APFS can be achieved when running the High Sierra installer directly from Mac OS or when using a macOS High Sierra boot installer drive.
Mac users who ran the beta of macOS High Sierra may remember earlier versions of the beta builds had a toggle setting during installation to skip APFS conversion, but that option toggle is no longer available in the installer.
Regarding APFS and macOS High Sierra, Apple says the following on a knowledge base support article:
“When you install macOS High Sierra on the Mac volume of a solid-state drive (SSD) or other all-flash storage device, that volume is automatically converted to APFS. Fusion Drives, traditional hard disk drives (HDDs), and non-Mac volumes aren’t converted. You can’t opt out of the transition to APFS.”
Despite the Apple support article saying that you can’t opt out of the transition to APFS, it turns out that you can skip APFS if you choose to start the installer from the command line of Mac OS and give a directive to skip file system conversion. Outside of using the Terminal approach outlined above, or installing on an HDD or Fusion drive, there is no known other method to skip APFS.
Again, there is no benefit or particular reason for most users to skip APFS conversion. Skipping APFS file system on a Mac with a flash drive means the computer won’t see the potential performance boost offered by APFS with High Sierra. This is really only for advanced users who need to skip APFS for a specific reason, usually for networking or drive sharing compatibility purposes.
MacOS High Sierra includes the all new APFS file system, which is arguably one of the most significant new features introduced in the new Mac operating system update. Nonetheless it’s possible that some Mac owners with SSD volumes will want to not convert the existing HFS+ file system to APFS file system when installing macOS High Sierra. With a little command line magic, you can skip converting to APFS during the macOS High Sierra installation process if desired.
How to Install macOS High Sierra Without Converting to APFS File System
This is not recommended and should only be applicable to advanced users who have specific reasons to not want to convert a Mac to APFS. APFS is faster and offers better encryption, amongst other benefits, so it’s generally recommended to use APFS if the Mac supports it. APFS is currently only supported on SSD drives, with Fusion drives support for APFS soon to arrive in a future Mac software update.
How to Not Convert to APFS During macOS High Sierra Installation
By skipping APFS conversion of file system, macOS High Sierra will install with the longstanding HFS+ file system instead.
1. Download the MacOS High Sierra installer from the App Store as usual, making sure it’s within the /Applications/ directory*
2. Open the Terminal application, found in /Applications/Utilities/ (or from the Utilities screen menu options if booted from a USB boot installer)
3. Enter the following command syntax at the command line prompt:
/Applications/Install\ macOS\ High\ Sierra.app/Contents/Resources/startosinstall --converttoapfs NO
4. Hit return key to start the macOS High Sierra install process with the –converttoapfs NO directive, thereby skipping the APFS conversion of existing file system
* You will need the full installer to have the Contents/Resources/ options available to you. You can download the full macOS High Sierra installer with these instructions if you’re getting the little mini-installer without /Content/Resorouces/ folder.
In case you were wondering, skipping APFS can be achieved when running the High Sierra installer directly from Mac OS or when using a macOS High Sierra boot installer drive.
Mac users who ran the beta of macOS High Sierra may remember earlier versions of the beta builds had a toggle setting during installation to skip APFS conversion, but that option toggle is no longer available in the installer.
Regarding APFS and macOS High Sierra, Apple says the following on a knowledge base support article:
“When you install macOS High Sierra on the Mac volume of a solid-state drive (SSD) or other all-flash storage device, that volume is automatically converted to APFS. Fusion Drives, traditional hard disk drives (HDDs), and non-Mac volumes aren’t converted. You can’t opt out of the transition to APFS.”
Despite the Apple support article saying that you can’t opt out of the transition to APFS, it turns out that you can skip APFS if you choose to start the installer from the command line of Mac OS and give a directive to skip file system conversion. Outside of using the Terminal approach outlined above, or installing on an HDD or Fusion drive, there is no known other method to skip APFS.
Again, there is no benefit or particular reason for most users to skip APFS conversion. Skipping APFS file system on a Mac with a flash drive means the computer won’t see the potential performance boost offered by APFS with High Sierra. This is really only for advanced users who need to skip APFS for a specific reason, usually for networking or drive sharing compatibility purposes.