I wanted to downgrade my Sonoma installation to Ventura on a Mac Studio. Before doing so I thought I’d take a full backup on an external drive using SuperDuper. This has worked great in the past, and I had assumed it would still work fine on Apple Silicone models in 2025.
MASSIVE mis-assumption! Of course things don’t work anymore as they did a decade ago before Big Sur came along. Apple are continuing to make using Macs for anything other than an iOS experience impossible, or at least so difficult that most of us do not even want to. HUGE amounts of sweat and tears need to be invested, carefully designed to stop users from fiddling and rely on the almighty Apple to take care of all our jailed computer needs. But I digress.
My external SuperDuper clone worked in principle, but the drive couldn’t boot. After several attempts and a black screen for like 15 minutes, my Mac Studio came back with “yeah erm no we sort of need to install the operating system again”. This is vague enough to foreshadow trouble, but it’s actually easier to deal with than I had expected.
So here’s how to make an external bootable clone with SuperDuper, which works for both Sonoma and Ventura.
It requires several hours of your time though, so be prepared for that and make yourselves comfortable. Here are the steps:
- make a backup with SuperDuper, as usual (this needs to be onto an APFS formatted drive, doesn’t have to be empty, but you need a separate volume on that drive to hold the backup. The HFS+ format won’t work anymore)
- in System Settings, search for Startup Drive and choose the external drive
- you need to pick an “authorised user” (i.e. yourself) on the external drive
- you’ll be prompted for your password about 67 times in a row
- when the password terror finally stops, your system will restart
Here’s where it gets slightly tricky: the Mac will appear to be dead, or if you’re unlucky enough to use a mechanical drive, it’ll appear to reboot several times in a row with no screen output. That’s perfectly normal. Eventually it’ll come up with a message that macOS needs to be re-installed, and you get an option to enter the Recovery Menu. This is what we want!
You’ll be prompted to re-install whatever version the clone was running, and the only way to get it is for Recovery to download this again in its entirety from the web. And because everyone in the world now has multi-gigabit internet connections, and slow connections have all been eradicated like small pox, this isn’t a problem and only takes 20 minutes… unless you’re in that 80% of humanity with a SLOW connection, in which case it’ll take a frigging hour or more. THANK YOU APPLE!
Now this is important: when it comes to selecting where to install the OS, pick the external hard drive (your boot clone). Don’t worry about data loss, it’ll all be intact afterwards. Let it noodle around, and eventually you’ll have to supply the password for your admin user and you have a running clone!
You only have to do this once, all subsequent Smart Updates of that external clone will work just fine as always.
About booting from external drives
Something I didn’t know here is that Apple in their “lock down madness” don’t actually allow booting from external drives as they did back in the day, at least on Apple Silicone hardware. Intel Macs – even models with T2 SecuriShite Chips – properly boot from external drives, but models with Apple M chips cannot, they always check the internal drive for some secure enclave yadayada. If this ever breaks, your $4000 Mac becomes a paperweight.
So while you can still “load data” and “run an OS” of a different version/configuration from an external drive, it’ll always use the bootloader from the internal drive, unless you have an old Intel Mac, which does not seem to do that.
Just one more thing: Sequoia issues
To make matters worse, enter macOS Sequoia (aka The Devil’s Release).
With version 15.2 of macOS, Apple have introduced a restriction that doesn’t allow people who make backup and cloning software to use anything other than one single utility to generate clones, a utility made by Apple. Before this change in Deceomber 2024, tools like Carbon Copy Cloner and Super Super could use their own routines to backup the operating system and boot logic. But no more, and that’s caused the makers of these tools a big of headaches.
This has since been resolved and these tools now can make full copies, but it shows just how much Apple are interested in these shenanigans to become more difficult or obsolete. I’m going stay as far away from Sequoia as I possibly can for the time being.
Good luck out there!
- SuperDuper by Shirtpocket: https://shirtpocket.com/superduper