Why to erase a disk
You can erase a disk (or a volume on that disk) at any time, including in circumstances such as these:
- You want to quickly and permanently erase all content from your Mac and restore it to factory settings, such as when you're selling or giving away your Mac.
- You're changing the format of a disk, such as from a PC format (FAT, ExFAT, or NTFS) to a Mac format (APFS or Mac OS Extended).
- You received a message that your disk isn't readable by this computer.
- You're trying to resolve a disk issue that Disk Utility can't repair.
- The macOS installer doesn't see your disk or can't install on it. For example, the installer might say that your disk isn't formatted correctly, isn't using a GUID partition scheme, contains a newer version of the operating system, or can't be used to start up your computer.
- The macOS installer says that you may not install to this volume because it is part of an Apple RAID.
How to erase a disk
Your Mac includes Disk Utility, an app that can erase disks, add volumes, check disks for errors, and more.
Erasing a disk or volume permanently deletes all of its files. Before continuing, make sure that you have a backup of any files that you want to keep.
- If you're erasing the disk your Mac started up from, start up from macOS Recovery before continuing. Or start up from a different disk.
- Open Disk Utility from the macOS Utilities window. You can also find it in the Utilities folder of your Applications folder.
- Choose View > Show All Devices from the menu bar.
- From the sidebar in Disk Utility, select the disk or volume to erase.
For most reasons to erase, you should erase the disk, which also erases all volumes on that disk.
- Click the Erase button or tab, then complete these fields:
- Name: Enter a name for the disk or volume, such as "Macintosh HD".
- Format: Choose either APFS or Mac OS Extended (Journaled) to format as a Mac volume. Disk Utility shows a compatible format by default.
- Scheme (if shown): Choose GUID Partition Map.
- Click Erase to begin erasing.
- Quit Disk Utility when done. You can now install macOS on the disk or volume, if you want your Mac to be able to start up from it.
In the following example, APPLE SSD is the disk, Container disk1 is a container on that disk, and Macintosh HD is a volume in that container. (Only APFS-formatted disks show containers.)
If your disk doesn't appear in Disk Utility, disconnect all nonessential devices from your Mac. If the disk is external, leave it connected, but make sure that it's turned on and connected directly to your Mac using a good cable. Then restart your Mac and try again. If your disk still doesn't appear, your disk or Mac might need service.
Which format to use: APFS or Mac OS Extended
Disk Utility in macOS High Sierra or later can erase most disks and volumes using either the newer APFS (Apple File System) format or the older Mac OS Extended format, and it automatically chooses a compatible format for you. 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, don't change it to Mac OS Extended.
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.
Will you be using the disk with another Mac?
If the other Mac isn't using High Sierra or later, choose Mac OS Extended (Journaled). Earlier versions of macOS don't mount APFS-formatted volumes.
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.
To learn which format is currently in use, use any of these methods:
- Select the volume in the Disk Utility sidebar, then check the information on the right. For more detail, 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.