Back up Your Startup Disk Using Disk Utility

Make a clone of your Mac startup disk

It's important to back up your startup disk before performing a system update. But how exactly do you do that?

In this guide, we detail one of many methods for backing up a startup disk. The process will take up to two hours or so, depending on the amount of data you need to back up.

How to Back up Your Startup Disk Using Disk Utility

Disk Utility restore tab
Disk Utility's Restore tab can create clones of your startup disk. Lifewire / Tom Nelson

We will use macOS' Disk Utility to perform the backup. It has two features that make for a simple procedure: First, it can produce a bootable backup, which you can use as a startup disk in an emergency. And second, it's free — included with every macOS computer.

What You Will Need

  • Disk Utility: A macOS app that can be found under /Applications/Utilities/.
  • An internal or external hard drive: You'll want a drive that is large enough to store the data on your current startup disk.
  • A destination drive: It's vital that this drive does not contain any data you'd like to keep. The method we will use erases 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 some factors that affect the use of the backup 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. Confirm that you can boot from an external device by creating a bootable backup of a macOS installer, and then 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; it will just require a few extra steps to restore the data.

Verify the Destination Drive With Disk Utility

The OS X backup preference panel
Be sure to verify and repair the destination disk, if needed, before you create your clone. Lifewire / Tom Nelson

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

Verify the Destination Drive

  1. Launch Disk Utility, located under /Applications/Utilities/.

  2. Select the destination drive from the device list.

  3. Select the First Aid tab.

  4. Select Run to check the volume for errors.

    In earlier versions of macOS, you may have to select Verify Disk.

After a few minutes, the following message should appear:

The volume {volume name} appears to be OK.

If you see this message, you can proceed 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.

  3. Select Repair Disk.

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 proceed to the next step.

If there are errors listed after the repair has finished, repeat the steps listed 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.

Check Disk Permissions of Your Mac's Startup Drive

Disk Utility in OS X
You should repair the disk permissions on the startup disk to ensure all files will be correctly copied to the clone. Lifewire / Tom Nelson

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. It's a good time to perform this routine maintenance task.

Repair Disk Permissions

  1. Select the startup disk from the device list in Disk Utility.

  2. Select the First Aid tab

  3. Select Repair Disk Permissions

The permissions repair process will begin. After a few minutes, you will receive a message that says, "Permissions repair complete." Do not be concerned if the Repair Disk Permission process generates a lot of warnings, as this is normal.

Start the Cloning Process of Your Mac's Startup Disk

Restoring from an image in Disk Utility
Drag the startup disk to the ‘Source’ field, and the target volume to the ‘Destination’ field. Lifewire / Tom Nelson

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. Select Restore.

During the process of creating the backup, the destination disk will be unmounted 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.

Check the Clone for the Ability to Boot up Your Mac

In order to confirm that your backup will work as a startup disk, you will 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. We'll do this because the choice made 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. From the Apple menu, select Restart...

  3. Wait for your screen to go black. Hold down the option key until you see a gray screen with icons of bootable hard drives. This can take some time, so be patient. If you're using a Bluetooth keyboard, wait till you hear the Mac's startup tone before you hold the option key.

  4. Select 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 is not 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 the external drive is using, such as FireWire or USB. See the first section of this guide for more information.