While it’s still possible to create an exact copy (a clone) of any drive connected directly to your Mac, changes to Disk Utility have created extra steps when you use Disk Utility’s Restore function to clone your startup drive. But don’t let the idea of extra steps get in the way, the process is still pretty simple, and the added steps actually help ensure a more accurate clone of the startup drive.
How Restore Works
The Restore function in Disk Utility uses a block copy function that can speed up the copy process. It also makes an almost exact copy of the source device. What “almost exact” means is that a block copy moves everything in a data block from one device to the other. The results are almost an exact copy of the original. A file copy copies the data file by file. While the information remains the same, the location of the file on the source and destination devices will likely be different. Using a block copy is faster, but it does have some limits that affect when it can be used, the most important being that copying block by block requires that both the source and destination devices be first unmounted from your Mac. This ensures that block data doesn’t change during the copy process. Don’t worry, though; you don’t have to do the unmounting. Disk Utility’s Restore function takes care of that for you. But it does mean that neither the source nor the destination can be in use when you use the Restore capabilities.
How to Restore a Non-Startup Volume
You can’t use the Restore function on the current startup drive, or any drive that has files in use. If you need to clone your startup drive, you can make use of either your Mac’s Recovery HD volume or any drive that has a bootable copy of OS X installed.
Restore Using a Startup Drive
When you use the Restore function, both the destination and the source must be able to be unmounted. Your startup drive can’t be active if you want to restore it. Instead, you can start your Mac from another volume that contains a bootable version of the Mac OS. The one you use can be any volume attached to your Mac, including a USB flash drive, an external, or the Recovery HD volume. A complete step-by-step guide is available in Use the Recovery HD Volume to Reinstall OS X or Troubleshoot Mac Problems.
Why Use Disk Utility’s Restore Function?
Disk Utility is free and included with every copy of the Mac OS. And while the various cloning apps have a lot more features, if you don’t have access to third-party apps, using Disk Utility will create a perfectly usable clone, although it may require a few more steps and lacks some nice features, such as automation and scheduling.
