From an email received from Mike Bombich:
macOS Big Sur and Carbon Copy Cloner backups
Apple will be shipping a major new operating system in the near future, and I wanted to take a moment explain how this change affects your CCC backups.
We recommend waiting for a few updates before upgrading to Big Sur because important components of the OS aren't working yet.
Early adopters can install macOS Big Sur onto the CCC backup volume to make it bootable.
What's changing in Apple's next OS upgrade?
With the announcement of macOS Big Sur, Apple has retired Mac OS X (10) and replaced it with macOS 11. As with every OS since the original release of Mac OS X, CCC has been adapted to accommodate the changes to this new OS. As the numeric change would suggest, though, this is the biggest change to macOS since Apple introduced Mac OS X roughly 20 years ago.
The system now resides on a "Signed System Volume". This volume is cryptographically sealed, and that seal can only be applied by Apple; ordinary copies of the System volume are non-bootable without Apple's seal. To create a functional copy of the macOS 11 System volume, we have to use an Apple tool to copy the system, or install macOS onto the backup.
Will CCC 5 work on macOS 11 or will I have to upgrade?
CCC 5.1.22 is qualified for use on macOS Big Sur, and that update is free for all CCC 5 license holders. Choose "Check for updates…" from the "Carbon Copy Cloner" menu and follow the instructions provided to apply the update.
Can CCC copy the macOS 11 System volume?
CCC will be able to use Apple's APFS replication utility ("ASR") to copy the System volume (we field-tested that functionality for the flawed 10.15.5 update). As of the latest Big Sur release, however, Apple's APFS replication utility is not working correctly with the Signed System Volume. As a result, ASR-created copies of the System volume are not bootable. Apple is aware of this issue and is currently working to resolve it.
Can I still make bootable backups on macOS 11?
Yes. There are two approaches to making your backups bootable on Apple's new OS. When Apple works out the problems in its APFS replication utility in an future update to macOS Big Sur, CCC will leverage that directly to copy the System volume and produce bootable backups. In the meantime, you can install macOS Big Sur onto your APFS-formatted CCC backup volume if you would like to make it bootable.
Does CCC back up all of my data, applications, and system settings?
Yes, absolutely. This part of CCC has not changed — CCC continues to provide complete backups of all of your data, applications, and system settings. Additionally, CCC offers support for snapshots, giving you access to older versions of your files. We design CCC to be a complete and more flexible replacement to Time Machine.
Does my CCC backup have to be bootable for me to restore data from it?
No. Bootability is a convenience that allows you to continue working if your startup disk fails, but it is not required for restoring data from a CCC backup. You can restore individual folders and older versions of files (i.e. from snapshots) using CCC while booted from your production startup disk. CCC backups are also compatible with Migration Assistant, so you can use Migration Assistant to restore all of your data to a clean installation of macOS (e.g. on a replacement disk).
Should I upgrade my Mac to macOS Big Sur?
Major system upgrades are often disruptive, so we have always recommended a very conservative approach to applying them. Consider the following:
Is the upgrade required for my Mac?
Will this upgrade improve the performance of my Mac, or degrade performance?
Does the upgrade provide some functionality that will make me more productive, or otherwise greatly increase my enjoyment of using my Mac?
Does the upgrade fix a problem that is preventing me from effectively using my Mac?
What software will no longer work after applying the upgrade?
If the upgrade turns out poorly and you have to downgrade, you certainly may downgrade using a CCC backup from an earlier OS. These sorts of procedures require time and effort, though, so you should weigh that potential hassle against the potential gain of the OS upgrade.
Lastly, we recommend that any users that rely heavily upon the availability of their Mac for work or other productivity consider waiting for several OS updates before making the upgrade. Early adopters inevitably find some shortcomings and bugs which are resolved in minor OS updates.
Related resources
Restoring from a bootable backup
Restoring from a snapshot
Migrating data from a data-only backup using Migration Assistant
Frequently asked questions about CCC and macOS Catalina (many of these are also applicable to Big Sur)
Best practices for updating your Mac's OS
macOS Big Sur Known Issues
We take pride in listening to our customers and strive to continually make CCC better. Do you have suggestions, requests, or questions? Just reply to this email and we'll take a look.
Mike Bombich
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