If you’ve read pretty much any book I’ve written about the Mac, you know I consider a solid backup plan to be essential for every Mac user. I hope you already perform backups regularly, and if you don’t, this is a perfect time to start.
Regardless of what you do normally (such as using Time Machine or Backblaze), I want to state emphatically that before upgrading to High Sierra, you should create a specific type of backup called a bootable duplicate. That’s an exact copy of everything on your startup volume, stored on another disk in such a way that you could start up your Mac from that other disk and it would behave precisely as it does when you boot from your regular startup volume.
Even though the High Sierra installer doesn’t force you to make this type of backup, it’s not something you can safely skip if it’s inconvenient or if you’re fairly sure you won’t have problems. In my professional opinion, creating a duplicate is a mandatory, integral part of the upgrade process. In this chapter I tell you both why and how to do this.
After you duplicate your startup volume, I’m going to tell you to do some spring cleaning (see Clean Up Your Mac), and then I’m going to tell you to update your duplicate. I wanted to warn you about this up front so you know it isn’t a mistake or capricious advice—it’s for your own good. You need a great backup before you delete any files (in case you accidentally delete something you need), but you also need a freshly updated backup right before installing High Sierra.
Let me also point out that whatever the virtues of Time Machine, it’s no substitute for a bootable duplicate, as I explain in the sidebar But I Really Don’t Want to Make a Duplicate!.
As I said, the particular type of backup you want at this moment—regardless of any other backups you may have—is a bootable duplicate, which is a clone or mirror image of everything on your startup volume. You can’t make a bootable duplicate in the Finder by dragging and dropping files onto another disk, and backup programs like Time Machine and Backblaze (though they’re both fantastic for what they do) can’t make them either. You must use a backup program that’s designed specifically for making a bootable duplicate.
Everyone should create a bootable duplicate and update it regularly (at least once a week) as part of a solid backup regimen. In day-to-day use, duplicates are important because they let you get back to work almost instantly in the event of a major disk error or even a complete failure of your hard drive or SSD. You simply plug in the backup drive, reboot while holding the Option key, and select the external drive, and you’re back up and running. You can then use the backup disk to repair your internal startup volume and restore your files—or if the drive is too far gone, replace it at your leisure.
However, aside from that “nice-to-have” reason for making a duplicate, you truly need one when it comes time to upgrade your operating system. Despite Apple’s valiant efforts at idiot-proofing the installer, something could go wrong—either during the upgrade or afterward—that deletes important files, leaves your disk unusable, or results in your needing to revert to your previous version of macOS. Bootable duplicates let you recover from these situations handily.
In addition, you may choose (for reasons discussed later, in Plan B: Clean Install) to erase your entire startup volume, install a clean copy of High Sierra, and then copy your personal files, third-party software, and other data back to your High Sierra volume. To be sure you have everything you might need during this process (and in exactly the right form), you must have a bootable duplicate.
To create a duplicate, you’ll need a few hardware and software ingredients, and you’ll need to follow a few preliminary steps.
You’ll need an empty hard drive for your duplicate. If you don’t happen to have an extra (internal or external) hard drive, take heart: hard drives are pretty cheap these days. For example, you can easily find a 4 TB external drive for less than $120, and compared to the cost of losing your data, that’s quite reasonable. Look for one with a fast interface (Thunderbolt 2 or 3, or USB 3), and with enough capacity to accommodate your growing backup needs over the next few years.
Many (but not all) backup apps can create bootable duplicates. If you don’t yet have a suitable tool, try Carbon Copy Cloner or SuperDuper. These two apps operate similarly and are easy to use.
You should create duplicates of your primary startup volume and any other volume on the same physical media. If you have a single, unpartitioned hard disk or SSD, then you have only a single volume to worry about. If you have multiple partitions (or multiple internal or external hard drives or SSDs) that contain bootable systems, I recommend making duplicates of all of them.
Before you can create your duplicate, you must perform a few quick steps to partition and format your disk. If the drive is already empty and properly formatted, you can skip these steps. But many new hard drives come formatted in a way that’s incompatible with bootable duplicates. (For example, I recently bought a 4 TB Seagate backup drive that came formatted as NTFS and included special software needed to use the drive on a Mac. That’s fine for ordinary backups, but it won’t work for a bootable duplicate.)
To prepare your drive, connect it to your Mac, turn it on, and launch Disk Utility (in /Applications/Utilities
). In the list on the left, select your external disk. (The disk is the topmost icon in any group, with any volumes it contains indented beneath it.) The remaining steps depend on which operating system your Mac is using.
Follow these steps in Disk Utility, with your external disk selected:
Disk Utility has now erased your disk and added any partitions that you specified. If you see an alert asking whether you want to use the new volume for Time Machine, click Don’t Use, since you’ll be using different software to create your bootable duplicate.
Follow these steps in Disk Utility, with your external disk selected:
Now that you’ve partitioned and formatted your disk, quit Disk Utility. If you see an alert asking whether you want to use the new volume for Time Machine, click Don’t Use, since you’ll be using different software to create your bootable duplicate.
Creating a bootable duplicate with either of my recommended utilities is quite easy: you simply choose a source disk (your existing startup volume) and a destination disk (your backup drive), specify a few options, and click a button. Although each backup app comes with its own instructions, here’s a quick overview of how to create a bootable duplicate with Carbon Copy Cloner ($39.99, free 30-day trial available), my personal favorite.
To create a duplicate with Carbon Copy Cloner, follow these steps:
Carbon Copy Cloner creates the duplicate and displays a message when your backup is complete. This process may take several hours or more (depending on the size and speed of your drive, among other factors).
Even if your backup app reported no errors, you should test the duplicate to make sure it truly is bootable before taking the plunge and upgrading to High Sierra. Follow these steps:
Be prepared to wait much longer than usual for your Mac to start up—as much as 10–15 minutes. Longer boot times are normal when starting a Mac from any new volume, but the time can be longer still if your backup drive uses a slow interface, such as USB 2.0.
You’ve just confirmed that your duplicate works correctly.