Disk Utility, in all of its incarnations, has always had a restore function, a way to copy a disk volume or image file to another volume, creating an exact copy. We often think of this as cloning a drive, so you have an exact copy for backup or archiving purposes.
The advantages of cloning are many, but the one that is repeatedly mentioned in troubleshooting guides, as well as guides to installing new versions of the Mac OS, is the clone’s ability to be used as a Mac’s startup drive. Provided the source for the clone was a bootable startup drive, then the destination will generally also be useable as a bootable startup drive, which is pretty darned convenient.
Disk Utility Restore
The restore function isn’t limited to creating clones of the startup drive. It can create a copy of any image or volume that can be mounted on your Mac. That makes the restore function extremely versatile, even if it’s largely overlooked in Disk Utility.
Two Versions of Disk Utility
Disk Utility was at version 16.0 at the time of this writing, so there have certainly been more than two versions. But when it comes to the restore feature, Disk Utility hasn’t undergone many changes; the biggest was the redesign of the Disk Utility interface that came about with the release of OS X El Capitan.
Because of that major change, we’re going to provide two sets of instructions for using Disk Utility’s Restore feature; one for OS X Yosemite and earlier, and one for OS X El Capitan and later.
What You Need
Restore will copy the source volume or image file to the destination volume, so you’ll need a disk that contains a volume large enough to hold the data from the source volume.
Both the source and destination volumes need to be mounted on your Mac. Restore will work with internal or external volumes.
If you’re planning on restoring from an image file you need to take the additional step of scanning the image file before the restore process. You’ll find instructions for preparing an image file near the end of this article.
Creating a Startup Clone
Using Disk Utility’s restore capabilities to make a clone of your startup drive has a limitation. Disk Utility uses a block copy method that provides for a faster copy, but it also needs to unmount all of the volumes involved in the restore process. Since the startup drive can’t be unmounted, you can’t make a clone of the startup drive directly.
Instead, you need to either boot your Mac to another drive that contains the Mac OS, or use the Recovery HD volume to start up and run Disk Utility from. This may seem like an inconvenience, but it provides for both a fast copy and a safe one; since the source drive can be unmounted, no process can make changes to any files resident on the drive.
Let’s start the step-by-step instructions with the current version of Disk Utility.
Using Restore With OS X El Capitan and Later
Go ahead and launch Disk Utility; you’ll find it at /Applications/Utilities/, or if you booted from the Recovery HD volume, Disk Utility will be one of the choices in the Utilities window.
In Disk Utility’s sidebar, select the destination volume you wish to have data copied to.
With the destination volume selected, click the Restore button in Disk Utility’s toolbar, or select Restore from the Edit menu.
A sheet will drop down, asking you to select the source volume. Use the dropdown menu next to the “Restore from:” text to select the source device, or use the Image button to select a disk image file.
Warning: The selected destination volume will be erased by the next step. If you need any of the information on the destination drive, make sure you have a backup before proceeding.
Click the Restore button in the dropdown sheet.
The restore process will begin; if you wish, you can view the process by clicking the disclosure triangle next to the “Show Details” text.
When the copy process is complete, click the Done button.
Copying using the restore function will also copy the volume title from the source to the destination, so you’ll now have two volumes with identical names. You may want to change the name of one of the volumes, to make it easier to tell them apart.
Using Restore With OS X Yosemite and Earlier
The earlier version of Disk Utility uses a slightly different user interface. Instead of selecting the destination first, as we did with the version in OS X El Capitan and later, we’re going to select the source volume first.
Launch Disk Utility, located in the /Applications/Utilities/ folder. If you’re booting from the Recovery HD volume, Disk Utility is listed in the OS X Utilities window, which opens automatically.
In the Disk Utility sidebar, select the volume you wish to use as the source. You can change this later if you select the wrong volume.
Click the Restore tab.
The volume you selected should be listed in the Source field. If you wish to change to a different source volume, select the desired source in the Disk Utility sidebar, or use the Image button to select a disk image file.
To select a destination, drag the desired volume from the sidebar to the Destination field. You can also drag a volume mounted on your Desktop to the Destination field.
Warning: The next step will completely erase the contents of the selected destination volume.
Click the Restore button.
A sheet will drop down, asking if you really want to completely erase the destination drive and replace its contents with the contents from the source drive. Click the Erase button to continue the restore process.
If requested, provide your administrator password, and then click OK.
The erase and restore process will begin; a status message and progress bar will appear near the bottom of the Disk Utility window.
When the restore is complete, the volumes will be remounted on your Desktop, and Disk Utility will remove the selected volume from the Destination field, leaving it empty.
The restore process also copies the source volume’s title to the destination volume; you may want to rename one or the other.
Restoring From an Image File (Any Version of Disk Utility)
Image files, those compressed .dmg files often used for distributing apps and data, can also be the source for the restore function. The process isn’t very different, except the image file needs to be prepared before it’s selected as the restore source.
The process scans the image file, calculates the checksum, and reorders the files within the image.
In Disk Utility, select Images, Scan Image for Restore.
Browse to where the image is stored, then select the image file and click the Open button.
Provide an administrator password, if asked, and then click the OK button.
When the scan is complete, click the Done button.
At this point, the image file can be used as the source in Disk Utility’s restore process.
Image File Limitations
Scanning an image file has a few limitations that can prevent some .dmg files from being properly scanned. Generally, if the image file uses the compressed format it should sail through the scan process. Read/write formats and hybrid images tend to cause errors. If you need to, you can convert the image file format using the Convert command in the Disk Utility Image menu.
For more handy tricks and guides, be sure to check out the Rocket Yard Tech Tips section.