Create and Use a Bootable Duplicate
Along with versioned backups, bootable duplicates are a key component of a complete backup plan. They let you get back to work quickly in the event of a hard drive failure, give you a useful troubleshooting tool, and make upgrading to a new version of macOS safer.
You can’t make a bootable duplicate by copying files in the Finder; you need a special utility. Lots of apps can do this, but in this chapter I focus on two—Carbon Copy Cloner and SuperDuper!—that specialize in this one task and do an excellent job at it.
Carbon Copy Cloner and SuperDuper! can make one-off duplicates, but they can also run automatically on a schedule, updating the duplicate with just the files that are new or changed since the last run, and deleting files on the destination that are no longer on the source disk. I recommend scheduling your duplicate to update itself at least once a week (daily is even better) as well as right before any macOS update.
I should mention that by default, making a duplicate of your startup disk will not also duplicate the hidden Recovery HD partition that Apple installs automatically with macOS. That is to say, if you boot from your duplicate or restore an entire disk from your duplicate, you won’t be able to use macOS Recovery unless you reinstall macOS on the disk—something you should never have to bother with if you have a bootable duplicate. That’s not a serious concern, though, in that the point of Recovery is to give you a way to repair and restore your Mac if you don’t have another bootable disk—a situation you won’t find yourself in if you have a bootable duplicate! However, Carbon Copy Cloner can duplicate the Recovery HD partition if you so choose; consult the app’s documentation for instructions. (Unfortunately, SuperDuper! can’t do this trick.) In addition, a free utility called Recovery Partition Creator can add a Recovery HD partition to an existing disk.
Give the Destination Volume a Unique Name
If you didn’t do so when partitioning the drive (see Configure Your Drive), rename the destination volume for your bootable duplicate so that it’s different from your Mac’s regular startup volume. This will help eliminate confusion later on, especially when you’re testing your duplicate and restoring files. To change the name, select the volume in the Finder, right-click (or Control-click) it, choose Rename “Volume Name” from the contextual menu, type a new name, and press Return.
Create a Duplicate with Carbon Copy Cloner
Carbon Copy Cloner was one of the first tools available for creating a bootable duplicate of a macOS volume, and it has undergone numerous revisions over the years.
Carbon Copy Cloner was originally designed only for creating bootable duplicates, but it has gradually added more features. It now also optionally creates versioned backups (although, to be honest, they’re not particularly easy to restore). To do this, Carbon Copy Cloner moves any outdated or deleted files safely aside on the destination disk—meaning the duplicate actually contains extra data, but that’s fine because the archived versions of old files won’t prevent booting or normal operation. Carbon Copy Cloner now has several other safety features too, which can protect you from the consequences of accidental file deletion.
In the instructions that follow, I deliberately avoid most of these safety features, and instead show you how to create a standard, run-of-the-mill duplicate that’s a true clone of the source volume. Consult the documentation that comes with Carbon Copy Cloner to learn about other ways of using the software to back up your disk.
To create a duplicate with Carbon Copy Cloner, follow these steps:
Launch Carbon Copy Cloner (Figure 17).
Figure 17: Carbon Copy Cloner shows you the basic elements of your backup—source, destination, options, and schedule—and a plain-English explanation. Click in the SOURCE area and select your startup volume from the popover that appears.
Click in the DESTINATION area and, from the popover that appears, select the disk or partition set aside for duplicates on your external disk.
Choose SafetyNet Off from the pop-up menu under DESTINATION.
Optional but recommended: click in the SCHEDULE area and, in the popover that appears, choose a frequency for scheduled updates of your bootable duplicate from the “Run this task” pop-up menu. Click Done.
Click Clone, enter your administrator password, and click OK to make an immediate duplicate. Then be prepared to wait; it will take a while.
Click Save when prompted to do so. You can then quit Carbon Copy Cloner. (In fact, you can quit even if a backup is in progress; Carbon Copy Cloner can finish the backup even when the app is not running.)
If you set up a schedule in step 5, Carbon Copy Cloner updates your duplicate automatically (as long as the drive is available).
Create a Duplicate with SuperDuper!
SuperDuper! has a well-deserved reputation for its ease of use and reliability. The software comes in a full-featured paid version and a free version that lets you create duplicates but not update them incrementally. (Let me say that the incremental update capability is well worth the price!)
To create a duplicate with SuperDuper!, follow these steps:
Launch SuperDuper!.
You’ll see two pop-up menus at the top of the window (Figure 18); choose the source (your internal disk) from the one on the left and the destination (the disk or partition set aside for duplicates on your external disk) from the one on the right.
Figure 18: Much like Carbon Copy Cloner, the SuperDuper! window asks you for just a few pieces of information, and clearly explains what will happen in plain English. From the “using” pop-up menu, choose “Backup - all files.”
If the lock icon in the lower-left corner is in the locked position, click it, enter your password, and click OK.
Click Options. In the General view, choose “Smart Update Destination from Source” from the “During copy” pop-up menu. Click OK. (Bear in mind that this option, which provides incremental updates, is available only in the paid version of SuperDuper!)
Do either of the following:
To make a duplicate immediately, click Copy Now, then click Copy to confirm that you really want to do this. (Be prepared to wait; your first duplicate will take quite a while.)
To set this duplicate to occur on a schedule, click Schedule and select the day(s), week(s), and time to run the schedule; I recommend at least one day per week but preferably once a day, at a time when you aren’t actively using the Mac. Click OK.
Immediately or on the schedule you selected, SuperDuper! duplicates your internal drive to your external drive.
Test Your Duplicate
After you’ve made your first bootable duplicate, be sure to verify that you can indeed start your Mac from it. To do this, follow these steps:
Make sure your bootable duplicate is connected to your Mac. Then restart your Mac by choosing Apple > Restart and clicking Restart when prompted.
Be aware that since you’re going to be switching to a different startup drive, deselecting the “Reopen windows when logging back in” checkbox may not have the desired effect; windows and apps may still reopen when your Mac finishes booting. If you want to avoid that, instead open System Preferences > Startup Disk, select your duplicate, and perform a safe boot. See the sidebar Perform a Safe Boot for details.
As soon as your Mac begins to restart, press and hold the Option key.
When your screen shows the volumes available for booting your computer, release the Option key, use the arrow keys to select your duplicate, and press Return. Your Mac should boot from the duplicate—but be aware that this may take considerably longer than booting from your regular startup disk; if your backup disk uses a slow interface, such as USB 2.0, it might take a very long time indeed.
To verify that your Mac has indeed started from the duplicate and not from your regular startup disk, choose Apple > About This Mac. The name of the current startup disk appears next to the label “Startup Disk.” (You did give your duplicate a different name from your regular startup disk, right?)
If you selected your duplicate as your startup disk in step 1, repeat the process to select your regular startup disk.
Choose Apple > Restart (without pressing any keys this time) to start from your internal disk again. Once again (as in step 4), confirm that you’ve booted from the correct startup disk; if you accidentally keep using your duplicate, problems and confusion could arise.
If your Mac does not start from the duplicate, go to System Preferences > Startup Disk, select the duplicate, restart, and again check to see that your Mac has started from the correct volume. (Be sure to set your startup disk back to its customary volume afterward!) If not, verify that the drive’s partition map scheme and format are correct (see Prepare Your Hard Drive) and try creating the duplicate again.