Back Up Your Startup Disk Using Disk Utility

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How to Back Up Your Startup Disk Using Disk Utility

Disk Utilities Restore Tab
Disk Utility's Restore tab can create clones of your startup disk. Screen shot courtesy of Coyote Moon, Inc.

You have probably heard the admonition to back up your startup disk before performing any system updates. That's an excellent idea, and something that I recommend often, but you may wonder just how to go about it.

The answer is simple: Any way you want, as long as you get it done. This guide will show you one of the many methods available for backing up a startup disk. ​The process takes half an hour to two or more hours, depending on the size of the data you're backing up.

I'll use OS X's Disk Utility to perform the backup. It has two features that make it a good candidate for backing up a startup disk. First, it can produce a backup that is bootable, so you can use it as a startup disk in an emergency. And second, it's free. You already have it, because it's included with OS X.

What You Will Need

  • Disk Utility, part of OS X and available at /Applications/Utilities/.
  • An internal or external hard drive that's large enough to store the data on your current startup disk.
  • A drive that doesn't contain any data you wish to keep. The method we will use will erase the destination drive during the backup process.

The destination hard drive can be an internal or external drive. If it's an external drive, there are two considerations that will determine whether the backup you create will be usable as an emergency startup drive.

  • FireWire external drives can be used as startup disks on both PowerPC-based Macs and Intel-based Macs.
  • USB external drives can be used as startup disks on Intel-based Macs, but not on PPC-based Macs. Some early USB 3 external drive enclosures did not always work as bootable sources. Be sure and check that you can boot from your external device. An easy way to make sure is to create a bootable backup of an OS X installer, and then try booting from your external.
  • Thunderbolt external storage works fine as a startup drive for any Mac that includes a Thunderbolt port.

Even if your backup drive isn't usable as a startup disk, you can still use it to restore your original startup drive if needed; it will just require a few extra steps to restore the data.

Published: 2/13/2008

Updated: 3/8/2015

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Before Cloning Verify the Destination Drive With Disk Utility

Back Up Your Startup Disk Using Disk Utility
Be sure to verify and repair the destination disk, if needed, before you create your clone.

Before you back up your startup drive, make sure the destination drive has no errors that could prevent a reliable backup from being made.

Verify the Destination Drive

  1. Launch Disk Utility, located at /Applications/Utilities/.
  2. Select the destination drive from the device list in Disk Utility.
  3. Select the 'First Aid' tab in Disk Utility.
  4. Click the 'Verify Disk' button.

The disk verification process will begin. After a few minutes, the following message should appear: “The volume {volume name} appears to be OK.” If you see this message, you can go on to the next step.

Verification Errors

If Disk Utility lists any errors, you will need to repair the disk before proceeding.

  1. Select the destination drive from the device list in Disk Utility.
  2. Select the 'First Aid' tab in Disk Utility.
  3. Click the 'Repair Disk' button.

The disk repair process will begin. After a few minutes, the following message should appear: “The volume {volume name} has been repaired.” If you see this message, you can go on to the next step.

If there are errors listed after the repair has finished, repeat the steps listed above under Verification Errors. Disk Utility can sometimes only repair a few types of errors in a single pass, so it may take multiple passes before you get the all clear message, letting you know that repairs are complete, with no remaining errors.

Find out more about using Disk Utility to test and repair drive problems.

Updated: 3/3/2015

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Check Disk Permissions of Your Mac's Startup Drive

Back Up Your Startup Disk Using Disk Utility
You should repair the disk permissions on the startup disk to ensure all files will be correctly copied to the clone.

Now that we know the destination drive is in good shape, let's make sure that the source drive, your startup disk, has no disk permission problems. Permission problems can prevent necessary files from being copied, or propagate bad file permissions to the backup, so this is a good time to perform this routine maintenance chore.

Repair Disk Permissions

  1. Select the startup disk from the device list in Disk Utility.
  2. Select the "First Aid" tab in Disk Utility.
  3. Click the 'Repair Disk Permissions' button.

The permissions repair process will begin. The process can take a few minutes, so be patient. When it's finished, you'll see a "Permissions repair complete" message. Do not be concerned if the Repair Disk Permission process generates a lot of warnings, this is normal.

Updated: 3/3/2015

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Start the Cloning Process of Your Mac's Startup Disk

Back Up Your Startup Disk Using Disk Utility
Drag the startup disk to the ‘Source’ field, and the target volume to the ‘Destination’ field.

With the destination disk ready, and your startup disk's permissions verified, it's time to perform the actual backup and create a replica of your startup disk.

Perform the Backup

  1. Select the startup disk from the device list in Disk Utility.
  2. Select the Restore tab.
  3. Click and drag the startup disk to the Source field.
  4. Click and drag the destination disk to the ‘Destination' field.
  5. Select Erase Destination.
  6. Click the Restore button.

During the process of creating the backup, the destination disk will be un-mounted from the desktop, and then remounted. The destination disk will have the same name as the startup disk, because Disk Utility created an exact copy of the source disk, down to its name. Once the backup process is complete, you can rename the destination disk.

You now have an exact replica of your startup disk. If you intended to create a bootable replica, this is a good time to ensure that it will function as a startup disk.

Updated: 3/3/2015

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Check the Clone for the Ability to Boot Up your Mac

In order to confirm that your backup will actually work as a startup disk, you'll need to restart your Mac and verify that it can boot from the backup. The easiest way to do this is to use the Mac's Boot Manager to select the backup as the startup disk. We will use Boot Manager, which runs optionally during the startup process, instead of the Startup Disk option in System Preferences, because the choice you make using Boot Manager only applies to that particular startup. The next time you start or restart your Mac, it will use your default startup disk.

Use Boot Manager

  1. Close all applications, including Disk Utility.
  2. Select "Restart" from the Apple menu.
  3. Wait for your screen to go black.
  4. Hold down the option key until you see a gray screen with icons of bootable hard drives. This can take a little time, so be patient. If you're using a Bluetooth keyboard, wait till you here the Mac's startup tone before you hold the option key.
  5. Click the icon for the backup you just made. Your Mac should now boot from the backup copy of the startup disk.

Once the desktop appears, you know that your backup is usable as a startup disk. You can restart your computer to return to your original startup disk.

If the new backup isn't bootable, your Mac will stall during the startup process, then after a delay, automatically restart using your original startup disk. Your backup may not be bootable because of the type of connection (FireWire or USB) an external drive uses; see the first page of this guide for more information.

Read about additional Startup Keyboard Shortcuts.

Updated: 3/3/2015