Erase a volume using Disk Utility on Mac
You can erase and reformat disks or volumes. Erasing a disk deletes everything on it. Erasing a volume deletes all the files on that volume, but does not affect other volumes.
If you have any files you want to save, copy them to another disk or volume before you erase the disk or volume they are on.
Open the Disk Utility app on your Mac using one of the following methods, depending on the type of disk or volume you want to erase:
If you want to erase your startup disk or startup volume: Start up from macOS Recovery, then choose Disk Utility from the macOS Utilities window.
If you want to erase any other type of disk or volume: Double-click Disk Utility in the /Applications/Utilities folder.
Choose View > Show All Devices.
Select the disk or volume in the sidebar, then click the Erase button .
If you’re erasing a disk, click the Scheme pop-up menu, then choose a partition scheme.
Click the Format pop-up menu, then choose a choose a file system format.
Enter a name for the disk or volume.
(Optional) If available, click Security Options, use the slider to choose how many times to write over the erased data, then click OK.
Secure erase options are available only for some types of storage devices. If the Security Options button is unavailable, Disk Utility cannot perform a secure erase on the storage device.
Writing over the data three times meets the U.S. Department of Energy standard for securely erasing magnetic media. Writing over the data seven times meets the U.S. Department of Defense 5220-22-M standard.
Click Erase, then click Done.
Note: With a solid-state drive (SSD), secure erase options are not available in Disk Utility. For more security, consider turning on FileVault encryption when you start using your SSD drive.