Until macOS 10.15 Catalina, Mac users knew: their startup volume was a single volume, just as it appeared! (Okay, for Fusion drive users, there are two physical drives managed by software to appear as a single “disk drive,” but that’s separate from the data organization that is a volume on a drive.)
As I wrote a couple of months ago, Apple relies on a feature in APFS (Apple File System) called “volume group.” This allows macOS to link together two separate volumes to appear as a single drive. Apple chose this method as a way to enhance security, putting read-only system files on one volume and your changeable data, home directory, preference files, and all the rest on another.
But where does this leave you if you want to clone your startup volume and create a backup that can be used as a one-stop shop for restoring a failed drive or Mac, or which can be booted from? Fortunately, all the software you need is up to date.
Time Machine correctly archives your entire startup volume (as well as other volumes you might specify), letting you restore a Catalina drive as you would a previous version of macOS.
SuperDuper! ($28) released version 3.3 in November with full Catalina backup and boot support. Its maker, Shirt Pocket Software, has never charged for updates, so if you own any previous release you can download and use the latest version.
This Mac 911 article is in response to a question submitted by Macworld reader John.
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