Mac Mini upgrade on a budget

Started 2 months ago | Discussions thread
Tom_N Forum Pro • Posts: 18,522
Re: Bootable clone of Big Sur

Jacques Cornell wrote:

Gesture wrote:

Will we be able to boot M1 Macs from an external drive? Thanks.

From what I've read & heard lately, cloning utilities are not currently able to create bootable clones of Big Sur. Devs are working with Apple to build a solution...

Clarification: Bombitch Software (CarbonCopyCloner) says you can make a bootable clone by first cloning your boot drive (which clones the data volume) and then installing Big Sur on it. I don't recall whether this works on M1 Macs or it's only for Intel Macs.

It's only necessary for M1-based Macs.

The issue comes about because in Big Sur, the System Volume has become a Sealed System Volume. Only Apple's code has the right cryptographic keys to sign it and to make it bootable (under default Startup Security Utility settings).

Apple's System Restore tool can clone the Sealed System Volume on Intel-based Macs on behalf of a program like CCC or SuperDuper.  But ASR's replication utility doesn't yet work on M1-based Macs.  It logs the error "'Apple System Restore Tool': Source volume format not yet supported in this version of macOS".

Thus, Carbon Copy Cloner 5.1.23 can make bootable backups of a Big Sur startup disk on Intel-based Macs, but not on M1-based Macs.  On M1-based Macs, if you want your clone to be bootable, you must do a Big Sur installation to fill in a Sealed System Volume.

Once Apple gets ASR working properly on M1-based Macs, and Bombich updates CCC to take advantage of that, the workaround will no longer be necessary.

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