Disk Utility User Guide

Disk Utility on Mac supports several file system formats:

• Apple File System (APFS): The file system used by macOS 10.13 or later.

• Mac OS Extended: The file system used by macOS 10.12 or earlier.

• MS-DOS (FAT) and ExFAT: File systems that are compatible with Windows.

Apple File System (APFS)

Apple File System (APFS), the default file system for Mac computers using macOS 10.13 or later, features strong encryption, space sharing, snapshots, fast directory sizing, and improved file system fundamentals. While APFS is optimized for the Flash/SSD storage used in recent Mac computers, it can also be used with older systems with traditional hard disk drives (HDD) and external, direct-attached storage. macOS 10.13 or later supports APFS for both bootable and data volumes.

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APFS allocates disk space within a container on demand. The disk’s free space is shared and can be allocated to any of the individual volumes in the container as needed. If desired, you can specify reserve and quota sizes for each volume. Each volume uses only part of the overall container, so the available space is the total size of the container, minus the size of all the volumes in the container.

Choose one of the following APFS formats for Mac computers using macOS 10.13 or later.

• APFS: Uses the APFS format.

• APFS (Encrypted): Uses the APFS format and encrypts the volume.

• APFS (Case-sensitive): Uses the APFS format and is case-sensitive to file and folder names. For example, folders named “Homework” and “HOMEWORK” are two different folders.

• APFS (Case-sensitive, Encrypted): Uses the APFS format, is case-sensitive to file and folder names, and encrypts the volume. For example, folders named “Homework” and “HOMEWORK” are two different folders.

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You can easily add or delete volumes in APFS containers. Each volume within an APFS container can have its own APFS format—APFS, APFS (Encrypted), APFS (Case-sensitive), or APFS (Case-sensitive, Encrypted).

Mac OS Extended

Choose one of the following Mac OS Extended file system formats for compatibility with Mac computers using macOS 10.12 or earlier.

• Mac OS Extended (Journaled): Uses the Mac format (Journaled HFS Plus) to protect the integrity of the hierarchical file system.

• Mac OS Extended (Journaled, Encrypted): Uses the Mac format, requires a password, and encrypts the partition.

• Mac OS Extended (Case-sensitive, Journaled): Uses the Mac format and is case-sensitive to folder names. For example, folders named “Homework” and “HOMEWORK” are two different folders.

• Mac OS Extended (Case-sensitive, Journaled, Encrypted): Uses the Mac format, is case-sensitive to folder names, requires a password, and encrypts the partition.

Windows-compatible formats

Choose one of the following Windows-compatible file system formats if you are formatting a disk to use with Windows.

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• MS-DOS (FAT): Use for Windows volumes that are 32 GB or less.

• ExFAT: Use for Windows volumes that are over 32 GB.

Erasing your disk: For most reasons to erase, including when reformatting a disk or selling, giving away, or trading in your Mac, you should erase your entire disk.

Erasing a volume on your disk: In other cases, such as when your disk contains multiple volumes (or partitions) and you don't want to erase them all, you can erase specific volumes on the disk.

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.

How to erase your disk

1. Start up from macOS Recovery. Then select Disk Utility from the Utilities window and click Continue.
   If you're not erasing the disk your Mac started up from, you don't need to start up from macOS Recovery: just open Disk Utility from the Utilities folder of your Applications folder.
   
2. Choose View > Show All Devices from the menu bar in Disk Utility. The sidebar now shows your disks (devices) and any containers and volumes within them. The disk your Mac started up from is at the top of the list. In this example, Apple SSD is the startup disk:
   
3. Select the disk that you want to erase. Don't see your disk?
4. Click Erase, then complete these items:
   • Name: Type the name that you want the disk to have after you erase it.
   • Format: Choose APFS or Mac OS Extended (Journaled). Disk Utility shows a compatible format by default.
   • Scheme: Choose GUID Partition Map.
5. Click Erase to begin erasing your disk and every container and volume within it. You might be asked to enter your Apple ID. Forgot your Apple ID?
6. When done, quit Disk Utility.
7. If you want your Mac to be able to start up from the disk you erased, reinstall macOS on the disk.

How to erase a volume on your disk

1. Start up from macOS Recovery. Then select Disk Utility from the Utilities window and click Continue.
   If you're not erasing the volume your Mac started up from, you don't need to start up from macOS Recovery: just open Disk Utility from the Utilities folder of your Applications folder.
2. In the sidebar of Disk Utility, select the volume that you want to erase. The volume your Mac started up from is named Macintosh HD, unless you changed its name. Don't see your volume?
3. Click Erase, then complete these items:
   • Name: Type the name that you want the volume to have after you erase it.
   • Format: Choose APFS or Mac OS Extended (Journaled). Disk Utility shows a compatible format by default.
4. If you see an Erase Volume Group button, the volume you selected is part of a volume group. In that case, you should erase the volume group. Otherwise, click Erase to erase just the selected volume. You might be asked to enter your Apple ID. Forgot your Apple ID?
   
5. When done, quit Disk Utility.
6. If you want your Mac to be able to start up from the volume you erased, reinstall macOS on that volume.

Reasons to erase

You can erase at any time, including in circumstances such as these:

• You want to permanently erase all content from your Mac and restore it to factory settings. This is one of the final steps before selling, giving away, or trading in 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.

About APFS and Mac OS Extended

Disk Utility in macOS High Sierra or later can erase 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.

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.
• Are you preparing a Time Machine backup disk or bootable installer?
  Choose Mac OS Extended (Journaled) for any disk that you plan to use as a Time Machine backup disk or as a bootable installer.
• Will you be using the disk with another Mac?
  If the other Mac isn't using macOS High Sierra or later, choose Mac OS Extended (Journaled). Earlier versions of macOS don't work with APFS-formatted volumes.

How to identify the format currently in use

If you want to know which format is currently in use, use any of these methods:

• Select the volume in the Disk Utility sidebar, then check the information shown 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.

If your disk or volume doesn't appear, or the erase fails

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1. Shut down your Mac, then unplug all nonessential devices from your Mac.
2. If you're erasing an external drive, make sure that it's connected directly to your Mac using a cable that you know is good. Then turn the drive off and back on.
3. If your disk or volume still doesn't appear in Disk Utility, or Disk Utility reports that the erase process failed, your disk or Mac might need service. If you need help, please contact Apple Support.

Learn more

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• If you can't start up from macOS Recovery, you can use a different startup disk instead.
• If Disk Utility shows a Security Options button in the Erase window, you can click that button to choose between a faster (but less secure) erase and a slower (but more secure) erase. Some older versions of Disk Utility offer the option to zero all data instead. These secure-erase options aren't offered or needed for solid-state drives (SSDs) and flash storage.