Disk Utility for Mac: Create a disk image using Disk Utility

Create a disk image using Disk Utility

Use Disk Utility to create disk images.

Note: You can burn information to a CD or DVD using the Burn command in the Finder. For more information, see Burn CDs and DVDs.

Create a blank disk image for storage

Create an empty disk image, fill it with data, then use it to create disks, CDs, or DVDs.

  1. Choose File > New Image > Blank Image.

  2. Enter a file name for the disk image, add tags if necessary, then choose where to save it.

    This is the name that appears in the Finder, where you save the disk image file before opening it.

  3. In the Name field, enter the name for the disk image.

    This is the name that appears on your desktop and in the Finder sidebar, after you open the disk image.

  4. In the Size field, enter a size for the disk image.

  5. Click the Format pop-up menu, then choose the format for the disk:

    • If the disk will be used with Mac computers, choose Mac OS Extended (Journaled) or Mac OS Extended (Case-sensitive, Journaled).

    • If the disk will be used with Windows or Mac computers and is 32 GB or less, choose MS-DOS (FAT).

    • If the disk will be used with Windows or Mac computers and is over 32 GB, choose ExFAT.

  6. To encrypt the disk image, click the Encryption pop-up menu, then choose an encryption option.

  7. Click the Partitions pop-up menu, then choose a partition layout.

  8. Click the Image Format pop-up menu, then choose an option:

    • Sparse bundle: Same as a sparse image, but the directory data for the image is stored differently. Uses the .sparsebundle file extension.

    • Sparse: Creates an expandable file that shrinks and grows as needed. No additional space is used. Uses the .sparseimage file extension.

    • Read/write: Allows you to add files to the disk image after it’s created. Uses the .dmg file extension.

    • DVD/CD master: Changes the size of the image to 177 MB (CD 8 cm). Uses the .cdr file extension.

  9. Click Save, then click Done.

    Disk Utility creates the disk image file where you saved it in the Finder and mounts its disk icon on your desktop and in the Finder sidebar.

  10. In the Finder, copy your files to the mounted disk image, then eject it.

  11. Restore the disk image to a disk.

Create a disk image from a disk or connected device

Create a disk image that includes the data and free space on a physical disk or connected device, such as a USB device. For example, if a USB device or volume is 80 GB with 10 GB of data, the disk image will be 80 GB in size and include data and free space. You can then restore that disk image to another volume.

  1. Select a disk, volume, or connected device in the sidebar.

  2. Choose File > New Image, then choose “Image from [device name].”

  3. Enter a file name for the disk image, add tags if necessary, then choose where to save it.

    This is the name that appears in the Finder, where you save the disk image file before opening it.

  4. Click the Format pop-up menu, then choose an option:

    • Read-only: The disk image can’t be written to, and is quicker to create and open.

    • Compressed: Compresses data, so the disk image is smaller than the original data. The disk image is read-only.

    • Read/write: Allows you to add files to the disk image after it’s created.

    • DVD/CD master: Can be used with third-party apps. It includes a copy of all sectors of the disk image, whether they’re used or not. When you use a master disk image to create other DVDs or CDs, all data is copied exactly.

  5. To encrypt the disk image, click the Encryption pop-up menu, then choose an encryption option.

  6. Click Save, then click Done.

    Disk Utility creates the disk image file where you saved it in the Finder and mounts its disk icon on your desktop and in the Finder sidebar.

Important: Don’t create a disk image of a disk that you believe to be failing or that contains corrupted information. The disk image may not serve as a reliable backup.

Create a disk image from a folder or connected device

Create a disk image that contains the contents of a folder or connected device, such as a USB device. This method doesn’t copy a device’s free space to the disk image. For example, if a USB device or volume is 80 GB with 10 GB of data, the disk image will be 10 GB in size and include only data, not free space. You can then restore that disk image to another volume.

  1. Choose File > New Image, then choose Image from Folder.

  2. Select the folder or connected device in the dialog that appears, then click Open.

  3. Enter a file name for the disk image, add tags if necessary, then choose where to save it.

    This is the name that appears in the Finder, where you save the disk image file before opening it.

  4. To encrypt the disk image, click the Encryption pop-up menu, then choose an encryption option.

  5. Click the Image Format pop-up menu, then choose an option:

    • Read-only: The disk image can’t be written to, and is quicker to create and open.

    • Compressed: Compresses data, so the disk image is smaller than the original data. The disk image is read-only.

    • Read/write: Allows you to add files to the disk image after it’s created.

    • DVD/CD master: Can be used with third-party apps. It includes a copy of all sectors of the disk image, whether they’re used or not. When you use a master disk image to create other DVDs or CDs, all data is copied exactly.

    • Hybrid image (HFS+/ISO/UDF): This disk image is a combination of disk image formats and can be used with different file system standards, such as HFS, ISO, and UDF.

  6. Click Save, then click Done.

    Disk Utility creates the disk image file where you saved it in the Finder and mounts its disk icon on your desktop and in the Finder sidebar.

Create a secure disk image

If you have confidential documents that you don’t want others to see without your permission, you can put them in an encrypted disk image.

Note: If you want to protect the contents of your entire home directory, turn on FileVault using the FileVault pane of Security & Privacy Preferences.

  1. Choose File > New Image > Blank Image.

  2. Enter a file name for the disk image, add tags if necessary, then choose where to save it.

    This is the name that appears in the Finder, where you save the disk image file before opening it.

  3. In the Name field, enter the name for the disk image.

    This is the name that appears on your desktop and in the Finder sidebar, after you open the disk image.

  4. In the Size field, enter a size for the disk image.

  5. Click the Format pop-up menu, then choose the format for the disk:

    • Mac OS Extended (Journaled)

    • Mac OS Extended (Case-sensitive, Journaled)

  6. Click the Encryption pop-up menu, then choose an encryption option.

  7. Enter and re-enter a password to unlock the disk image, then click Choose.

    WARNING: If you forget this password, you won’t be able to open the disk image and view any of the files.

  8. Use the default settings for the rest of the options:

    • Click the Partitions pop-up menu, then choose Single partition - GUID Partition Map.

    • Click the Image Format pop-up menu, then choose “read/write” disk image.

  9. Click Save, then click Done.

    Disk Utility creates the disk image file where you saved it in the Finder and mounts its disk icon on your desktop and in the Finder sidebar.

  10. In the Finder, copy the documents you want to protect to the disk image.

  11. If you want to erase the original documents so they can’t be recovered, drag them to the Trash, then choose Finder > Empty Trash.

When you’re finished using the documents on the secure disk image, be sure to eject the disk image. As long as it’s available on your desktop, anyone with access to your computer account can use the documents on it.

To access the data in a disk image, double-click it. It appears on your desktop, and you can add, remove, and edit files on it just as you would with a disk.

Published Date: Sep 22, 2016
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