Disk Utility provides four options for securely erasing the data on a volume. The options include a very basic erase method, a slightly more secure erase method, and two erase methods that meet or exceed U.S. Department of Defense requirements for erasing confidential data from hard drives.
If you're concerned about someone being able to recover the data you're about to erase, use the secure erase method outlined below.
Secure Erase
- Select a volume from the disks and volumes listed in the left side of the Disk Utility window. Each disk and volume will be identified by the same name and icon that it displays on the Mac desktop.
- Click the ‘Erase’ tab. The selected volume's name and current format will display in the right side of the Disk Utility workspace.
- Click the ‘Security Options’ button. A Security Options sheet will display the following secure erase options.
- Don’t Erase Data. This method is quick, but not very secure. It removes the volume's catalog directory, but leaves the actual data intact.
- Zero Out Data. This method provides a good level of security. It erases the volume's data by writing over it with zeros. The length of time this method takes depends on the size of the volume.
- 7-Pass Erase. This method meets the security requirements of the U.S. Department of Defense's 5220-22M standards for erasing magnetic media. This erase method can take a very long time.
- 35-Pass Erase. This is the highest level of data erase security that Disk Utility supports. It writes over the data on a volume 35 times. Don't expect this erase method to finish any time soon.
- Don’t Erase Data. This method is quick, but not very secure. It removes the volume's catalog directory, but leaves the actual data intact.
- Make your selection and click the ‘OK’ button. The Security Options sheet will disappear.
- Click the ‘Erase’ button. Disk Utility will unmount the volume from the desktop, erase it, and then remount it on the desktop.
