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Disk Utility 12.x: Erase a disk, CD, or DVD

Erase a disk, CD, or DVD using Disk Utility

You can erase a disk so you can use it again. If it contains confidential data, you can securely erase it to prevent the data from being recovered. You can also securely erase a disk’s empty space, which prevents the recovery of erased files without erasing the entire disk.

Erase a disk

You can erase disks or partitions. Erasing a disk deletes all its partitions and files. Erasing a partition deletes all the files on that partition, but does not affect other partitions.

To erase your computer’s startup disk, you must start up from another disk, such as a Mac OS X installation disc.

Important: If you have any files you want to save, be sure to copy them to another disk before you erase the disk they are on.
  1. Open Disk Utility, in the Utilities folder in Launchpad.
  2. Select the disk or partition and click Erase.
  3. Choose a format from the Format pop-up menu. Usually you will choose Mac OS Extended (Journaled).
  4. Type a name for the disk or partition.
  5. If you want to prevent the erased files from being recovered, click Security Options, select the option you want, and click OK.
  6. Click Erase.

Erase a CD-RW or DVD-RW disc

You can erase a rewritable CD or DVD so you can reuse it.

  1. Open Disk Utility, in the Utilities folder in Launchpad.
  2. Insert the disc into your computer’s optical drive or an optical drive connected directly to your computer.

    You can’t burn a disc using a remote optical drive.

  3. Select the disc and click Erase.
  4. If you haven’t been able to save to or read from the disc reliably, select Completely. Otherwise, select Quickly.

    Quickly erasing a disc takes a few minutes. Completely erasing it can take about an hour.

  5. Click the Erase button.

Securely erase a disk

You can securely erase a disk or partition to make sure the confidential information it contains cannot be recovered.

When erasing a disk or partition, Disk Utility does not erase the actual files; it erases only the information used to access the files. Many commonly available disk recovery applications can easily recover the files. When securely erasing a disk or partition, Disk Utility writes over the erased files, so they can never be recovered. You can choose how many times to write over the files. Writing over the files several times is more secure than writing over them once, but takes longer.

Securely erasing a disk erases files on all its partitions. Securely erasing a partition erases all the files on that partition but does not affect other partitions.

You can’t securely erase a CD, DVD, or a solid-state drive. If you don’t want data recovered from a solid-state drive, use full disk encryption.

To erase your computer’s startup disk, you must start up from another disk, such as a Mac OS X installation disc.

  1. Open Disk Utility, in the Utilities folder in Launchpad.
  2. Select the disk or partition to erase, and then click Erase.
  3. Specify a format, and enter a name for the disk.
  4. Click Security Options, use the slider to choose how many times to write over the data on the disk, and click OK.

    Writing over the data 3 times meets the U.S. Department of Energy (DoE) standard for securely erasing magnetic media. Writing over the data 7 times meets the U.S. Department of Defense (DoD) 5220-22-M standard.

  5. Click Erase.

Erase free disk space

When you delete files by emptying the Trash, Mac OS X deletes the information used to access the files but doesn’t actually delete the files. Although the disk space used by deleted files is marked as free space, deleted files remain intact until new data is written over them. As a result, deleted files can be recovered.

You can use Disk Utility to erase the free space used by deleted files by writing over the space one or more times. If you have a lot of free space on your disk, overwriting the free space several times can take a long time.

Erasing free disk space does not erase the other files on your disk.

  1. Open Disk Utility, in the Utilities folder in Launchpad.
  2. Select the disk or partition with the free space you want to erase.
  3. Click Erase, and then click the Erase Free Space button.
  4. Use the slider to choose how many times to write over the free space, and then click Erase Free Space.

After the process begins, you can interrupt it without harming your data.

You might see a message that says you’re running out of disk space, but you can ignore that warning.

When this operation is complete, your disk should have the same amount of free space as it did beforehand. If you have less space, choose Apple menu > Restart, and the remaining space should be recovered.

Last Modified: Jul 11, 2012
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  • Last Modified: Jul 11, 2012
  • Article: PH5849
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