Whether you need to organize your hard drive better or troubleshoot disk errors, Disk Utility is the tool for you. Built into macOS, Disk Utility is hidden in the Utilities folder, which is inside the Applications folder, but is easy to locate using Spotlight — which you trigger by pressing Command-Spacebar, then just type Disk Utility.
The tool displays details and a graph of your hard drive configuration, showing the overall capacity as well as used and free space and the various volumes.
Over the years, Disk Utility has been revised several times, so the options may be slightly different depending on the version of macOS you’re using. For example, in Mac OS X, El Capitan Disk Utility has been redesigned and many features have evolved or been removed. There have also been some changes in macOS High Sierra thanks to the new file format introduced by Apple: APFS. And when Catalina arrived, a new Macintosh HD – Data volume started showing up next to a read-only Macintosh HD system volume.
Why Use Disk Utility
You can use Disk Utility to do the following:
Erase, format or manage internal drives and external storage devices. (Read: How to format a disk on a Mac)
Diagnose and resolve issues with damaged disk or volumes. (See: How to Check Your Mac’s Disk Integrity Using Disk Utility).
To erase, format or partition a disk or volume. (See: How to partition a Mac drive or create an APFS volume).
To encrypt storage devices or add a password to protect a drive.
To mount, unmount or eject a disc.
To change the file system – for example to enable or disable journaling.
Work with RAID sets. Combining multiple disks in a RAID set that acts as a single disk can increase performance, reliability, and storage space.
Create a disk image of files you want to move to another computer, archive, or back up.
Disk Utility used to be used to check and repair permissions, but since El Capitan this is no longer needed.
You may want to use Disk Utility if you experience the following issues:
Below, we’ll see how to perform the most common Disk Utility tasks.
How to tell if your disk is bad using Disk Utility
If you think there’s a problem with the drive inside your Mac or an external storage device, you can use the First Aid feature in Disk Utility to check.
Disk Utility’s First Aid feature will run various checks and if it finds a problem with your disk, it will repair it.
Note that you cannot use First Aid to repair your startup drive while it is running the operating system. We will see how to proceed next.
Here’s how to run First Aid on your Mac or an external drive to check if there’s a problem with the drive:
Open Disk Utility.
Select your device you’re having trouble with from the sidebar. Click Show all devices (in the drop-down menu above Show) if you don’t see it.
Click on First Aid.
Disk Utility will check the volume for errors and repair it if necessary. Click Run.
While Disk Utility is checking the volume, you won’t be able to use your Mac – be aware that this can take a long time.
If it detects a problem with the disk, Disk Utility will attempt to repair it.
If Disk Utility fails to repair the drive or thinks the disk is about to fail, it will warn you. If so, you need to back up your data before it’s too late. Read this article on backing up your Mac. You may also find this useful: How to Recover and Delete Data from a Failed Hard Drive, SSD or External Drive.
If Disk Utility reports that the disk is OK, there is no problem with the disk.
How to Repair Your Startup Disk/Startup Disk with Disk Utility
You can run First Aid on your startup drive by following the steps above, but if Disk Utility finds any errors, it won’t try to fix them.
If you need to repair your Mac’s startup drive (the startup volume), you won’t be able to because Disk Utility can’t repair the mounted volume (the one everything is running from).
In this case, you need to boot your Mac into recovery mode and repair the disk from there. This way things can work from the Recovery HD volume that was created when installing macOS.
The method of accessing Recovery depends on your Mac:
If you have an M1-series Mac, shut down the Mac, then press and hold the power button while it boots up.
If you have an Intel Mac, restart your Mac and hold down Command-R on the keyboard.
We have a detailed tutorial on how to use recovery mode here.
To repair your startup disk:
Boot into Recovery by following the steps above.
Once your Mac has booted into Recovery, you’ll see a Utilities screen. Choose Disk Utility.
Select the disk you want to repair from the menu and click on First Aid.
As above, Disk Utility will run its checks and attempt to repair if it can.
The repair process may take some time.
For more information, read How to Check Your Mac’s Disk Health Using Disk Utility.
How to Format a Disk Using Disk Utility
There are a number of reasons you might want to format a drive. Maybe you want to erase your startup drive so you can do a clean install of OS X, maybe you want to encrypt an external storage drive you use for work, or create a partition for Windows or some version different from the Mac operating system.
There are different file formats you might want to use, including:
Apple File System (APFS) – Apple’s file system since macOS 10.13.
Mac OS Extended – Apple’s filing system prior to macOS 10.13.
and MS-DOS (FAT) and ExFAT – for compatibility with Windows.
We have a step-by-step guide to formatting a drive on Mac here.
When you format a disk, you can also add encryption and other security features.
How to Use Disk Utility When a Drive Won’t Mount
If you plug a hard drive or flash drive into your Mac and you can’t see it and won’t let you access the read data: what to do if a hard drive won’t mount.
How to Create a Disk Image Using Disk Utility
Disk Utility is able to create a disk image of the contents of a folder that you can then transfer to another Mac, an archive, or any location that doesn’t accept folders.
This is similar to compressing the folder into a zip archive, but the advantage is that you can not only use disk image compression to save space, but also take advantage of Apple’s encryption for the disk image.
Follow these steps to create a disk image using Disk Utility.
How to partition a disk or create a volume
You may want to partition a disk to divide it into separate containers or because you want to install multiple operating systems. How you do this will depend on the version of macOS you’re using. On newer Macs rather than creating a partition, you need to create a volume.