Disk Utility in macOS High Sierra or later versions can erase most of your disks and volumes using the latest Apple File System (APFS) format or the previous extended Mac OS format and automatically choose a format that is compatible for you. If you want to change the format, answer these questions:
Are you formatting the built-in disk in your Mac?
If the embedded disk is formatted with APFS, do not change it in Mac OS Extended.
Are you about to install MacOS High Sierra or later on the disc?
If you need to erase the 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 deleting the files:
- macOS Mojave: the installer is converted from Mac OS Extended into APFS.
- macOS High Sierra: the installer is converted 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) are not converted.
Are you preparing a Time Machine backup disk or a bootable installer?
Choose Mac OS Extended (Journaled) for any disk you wish to use with Time Machine or as a bootable installer.
Will you use the disk with another Mac?
If the other Mac does not use High Sierra or later, choose Mac OS Extended (Journaled). Older versions of macOS do not mount volumes formatted in APFS.
Disk Utility tries to detect the type of storage and shows the appropriate format in the Format menu. If you can not, choose Mac OS Extended, which works with all versions of macOS.
To find out which format is currently in use, use one of these methods:
- Select the volume in the Disk Utility sidebar, and then check the information on the right. For more details, choose File> Get Info from the Disk Utility menu bar.
- Open System Information and select Storage in the sidebar. The File system column on the right shows the format of each volume.
- Select the volume in the Finder, then choose File> Get Info from the menu bar. The Get Info window shows the format of that volume.