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Disk Utility is an important tool on your Mac that you can find in the Utilities folder. It does many useful things like partitioning disks, fixing issues, completely erasing disk, and reformatting. But sometimes, Mac users face a problem: they can’t use Disk Utility to erase a disk.

This issue shows up when the option to erase a disk in Disk Utility is grayed out and can’t be clicked, or when the erasing process doesn’t work. No matter why this happens, We’re here to help you figured out what to do next.

Part I. What if the Erase Button in Disk Utility is Grayed out?

If you’re trying to erase the disk that your computer is currently using to start up, it won’t work. To erase your main disk, you have to boot into Recovery mode to format the Mac startup disk. Recovery Mode on a Mac is a special environment that provides various tools and options to troubleshoot and manage your computer. It’s useful for tasks like reinstalling macOS, restoring from backups, repairing disk issues, and more.

Follow the steps below to completely erase your Mac hard drive

1. Boot into Mac Recovery Mode first. 

• For Intel-based Mac users: Restart your Mac, then hold Command + R keys until you see the Apple logo or hear a startup sound.
• For M1 Mac users: Turn off your computer, and press the power button until the Options Menu shows up, and then click Option > Continue.

2. Select a language and your account, and then enter the correct password.
3. Select Disk Utility from the Utilities window.
4. Select Macintosh HD – Data, press the minus (-) sign, and then tap “Delete” to confirm removing it. (If you have macOS Mojave or an earlier version, you can ignore this step.)
5. Choose “Macintosh HD” and then click on the Erase button.
6. Give your hard drive a name (such as “Macintosh HD”), select APFS for macOS 10.13 and later, or Mac OS Extended for macOS 10.12 and earlier. Keep the Scheme as GUID Partition Map.
7. Finally, just click on the “Erase” button and wait for a while as the selected drive would be erased.

One small tip: For a smoother process and to prevent the “Secure Disk Erase Failed – Couldn’t Unmount Disk” error, it’s advisable to erase the volume rather than the entire disk.

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Part II. Troubleshooting When Disk Utility Can’t Erase “Macintosh HD

Solution1. Fix the startup disk using Disk Utility’s First Aid feature

1. Open Disk Utility and pick the disk you want to erase (if it’s not visible, go to the View menu and choose “Show All Devices”).
2. Click on “First Aid” in the toolbar.
3. Press Run.
4. Allow Disk Utility to complete the disk repair. The time it takes for First Aid to diagnose your drive depends on its size, the data it holds, and the possible number of errors.

After the process finishes, you can attempt the erasure again.

Solution 2. Shift to Internet Recovery Mode to Format the Drive

Internet Recovery Mode works similarly to the regular Recovery mode, but with a twist. It doesn’t rely on the recovery partition within your Mac; instead, it connects to Apple’s Internet Recovery server to fetch the necessary disk image to initiate recovery mode.

While the added step of downloading the disk image might take some time, many users have found success erasing their Mac’s hard drive when the standard Recovery Mode didn’t work. Once you’re in Internet Recovery, you can follow the same steps to erase the Mac’s hard drive, just as you would in the regular Recovery mode.

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Part III. How to Resolve the ‘Erase Process Has Failed’ Error on Mac?

When Disk Utility faces issues erasing a drive, it might show the message “Erase process has failed. Click Done to continue.” This error could have more details like “couldn’t open device (-69877)” or “couldn’t unmount disk: (-69888).”

The “erase process has failed” error can arise due to various factors, including the corruption or unavailability of the Mac’s hard disk, the presence of malware or viruses on the system, interruptions caused by unplugging an external device during formatting, attempts to format non-existent volumes within Mac HD, security-related issues, an outdated macOS version, and incomplete initialization of critical Disk Utility components.

Before moving forward, take these steps into account: Close any open applications and files, conduct a malware scan and eliminate any identified threats, temporarily disable your security software, clean up your Mac, and finally, restart your computer. Once these tasks are completed, you can proceed to the solutions outlined below.

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1) Erase Selected Volume Instead

When you perform a disk erase, you are dealing with the data contained in all of its volumes. If any issues arise with one of these volumes, it can hinder the erasure of the entire disk.

Thus, if you encounter difficulties erasing the entire disk, consider attempting the erasure process on the individual volumes within it. This approach helps you ascertain whether the issue pertains to a particular volume.

2) Forcibly Unmount a Disk via Terminal App

It’s important to be aware that forcibly unmounting a disk carries the risk of potential data loss. Therefore, exercise caution and carefully follow the instructions below to ensure you’re unmounting the correct drive.

1. Launch Terminal by navigating through Launchpad > Other folder > Terminal.
2. Input the following command to display a list of connected drives on your Mac and press Enter: diskutil list

3. Take note of your Device Node for the subsequent step.
4. Execute the subsequent command to unmount your disk and press Enter:

sudo diskutil unmountDisk force device node

For instance, if your disk node is /dev/disk0, the command line will be: sudo diskutil unmountDisk force /dev/disk0

5. If prompted, enter your account password.
6. Exit Terminal after receiving a success report.
7. Launch Disk Utility, select the target drive, and initiate the Erase process once more to carry out the formatting.