Apple Silicon Macs: Bootable copies cannot be created of macOS Sequoia 15.2. This functionality was restored in macOS Sequoia 15.3.
Copying Apple's system is an Apple-proprietary endeavor; we can only offer "best effort" support for making an external bootable device on macOS. We present this functionality in support of making ad hoc bootable copies of the system that you will use immediately (e.g. when migrating to a different disk on Mac with replaceable or upgradable internal storage, or for testing purposes). External boot is not a reliable partner in a back up and recovery strategy. We do not recommend that you rely on it for that purpose.
Please bear in mind that you can restore all of your documents, applications, and system settings from a standard CCC backup without the extra effort involved in establishing and maintaining a bootable device.
In the past, a "bootable backup" was an indispensable troubleshooting device that even novice users could rely upon in case their production startup disk failed. Unfortunately, however, the creation of bootable backups is fundamentally incompatible with platform security. Further, Apple Silicon Macs will not start up (at all) if the internal storage is damaged or otherwise incapacitated, so there is very little value, if any, to maintaining a bootable rescue device for those Macs.
Making a copy of the startup disk with Apple Software Restore
The Backup Volume Setup Assistant is presented automatically when you select a destination volume. To present it again for a volume that is already selected, click on the Destination selector and choose Backup Volume Setup Assistant…. To configure CCC to create a bootable copy of your Mac's startup disk, choose the Legacy bootable clone using Apple Software Restore option, then click the Allow CCC to erase '(destination)' button.
Things you should know before relying on an external macOS boot device
This procedure relies on Apple's proprietary APFS replication utility, which is outside of our developmental control. We welcome feedback on this functionality, but we cannot offer in-depth troubleshooting assistance for problems that Apple's replication utility encounters.
- Whether the destination is bootable depends on the compatibility of your Mac, macOS, and the destination device. We cannot offer any troubleshooting assistance for the bootability of the destination device beyond the suggestions offered in our External Boot Troubleshooting kbase article.
- The destination may not remain bootable if you change the task configuration to perform "Standard" backups to the destination (i.e. via the Backup Volume Setup Assistant).
- Apple Silicon Macs: Apple's replication utility may fail to produce a bootable USB device. Results with Thunderbolt devices are more consistent. If you only have a USB device, we recommend making a Standard Backup to that device, then install macOS onto the backup (in that order specifically).
- Apple Silicon Macs will not boot at all if the internal storage fails. An external bootable device will not serve as a rescue disk for that scenario.
For the reasons noted above, we do not recommend that you attempt to make your backups bootable; we recommend that you proceed with a "Standard Backup" instead. You can restore all of your documents, compatible applications, and settings from a standard CCC backup without the extra effort involved in establishing and maintaining a bootable device.
Frequently Asked Questions
When the task started running, the destination was renamed to the same as the source. And what's this "ASRDataVolume" volume?
Highly perceptive people may notice that the name of the destination volume changes as Apple's volume replicator goes to work. An additional volume may appear in CCC's sidebar as well. This is normal. These volumes will be aggregated into a "volume group" and presented as a single volume, and CCC will rename the destination to its original name when the replication is complete.
If Apple's APFS replication utility fails and you see an ASRDataVolume or ASRNewVolume persisting, then you may delete those vestigial volumes in Disk Utility. Simply select the volume, then click the "-" button in the toolbar.
Do I have to erase the destination to make a bootable copy of the system?
Yes. The macOS system volume can only be copied by Apple ASR utility, and that utility only works by erasing the destination. You must dedicate a volume to your bootable copy of the system.
Can I use the destination device for storing other data as well?
On a separate, dedicated volume, yes. We recommend that you add an APFS volume to the destination APFS container and use that new volume for your other content. As long as the system copy and the other content are stored on separate volumes, these can coexist peacefully on the same physical device. Likewise, you may add a partition to your destination disk if the destination is not APFS formatted. For example, if you have an external hard drive that already has content on an HFS+ formatted volume, you can add a partition to the disk and use the new partition for the copy of the system.
Related documentation
If I continue to make regular backups to the destination, will it remain bootable?
If you keep the task configured to copy the source via Apple Software Restore and run the task regularly (i.e. via manual or scheduled backups), the copy should remain bootable. If you change the configuration of the task via the Backup Volume Setup Assistant to a "Standard Backup", then the destination may not remain bootable.
Can I exclude some content when making a bootable copy of the system?
No. The macOS system volume can only be copied by Apple ASR utility, and that utility can only make a complete, byte-for-byte exact copy of the startup disk. If you must exclude content from the initial copy, then we recommend that you proceed with a Standard Backup.
I already have other volumes on my backup disk. Will those be erased?
No, only the selected destination volume will be erased when you proceed with the "Allow CCC to erase {destination}" option. Other volumes on the same physical device will be unaffected. Regardless, we never recommend that you target a disk that has data on it that is not backed up elsewhere. If those other volumes are not yet backed up, then back up that data before proceeding.
I added a volume, but I don't want the extra volume after all. Can I delete it?
Yes. Choose Disk Utility from CCC's Utilities menu, select the volume you would like to delete, then press the "–" button in the toolbar to delete that volume.
Can I make the system copy on an encrypted volume?
You may select an encrypted volume as the destination, but the volume will be erased, and will not be encrypted when the task completes. Apple's APFS replication utility will not preemptively enable FileVault on the destination volume. To enable FileVault on the destination, you can boot from the system copy and enable FileVault in System Settings > Privacy & Security > FileVault.
Related documentation
You can install macOS onto a "Standard Backup" to make it bootable
We recommend using the Legacy bootable clone using Apple Software Restore option any time you have an immediate need to create a bootable copy of your startup disk. However, if some time in the future you find a need to boot from an external device, and you have an existing Standard Backup on a non-encrypted APFS volume that you would like to make bootable, you can install macOS onto that volume:
- Download and open the macOS Installer: [Ventura] [Sonoma] [Sequoia]
- When prompted to select a disk, click the Show All Disks... button and select your backup disk
- Proceed to install macOS onto your backup disk
Note that the macOS Installer will remove any snapshots on the backup volume, thus revoking any opportunities to restore older versions of your files.
Troubleshooting tip: Some users have discovered that macOS will stall when starting up from the backup disk. If you encounter this problem, try booting in Safe Boot mode (Intel Macs: hold down the Shift key on startup, Apple Silicon Macs: hold down the Power button on startup, then press the Shift key while selecting the startup volume) to disable the loading of third-party storage drivers. If applicable, see this Kbase article to see how to uninstall incompatible third-party storage drivers.
Please note, however, that our recommended procedure for restoring your startup disk from a CCC backup is to install macOS onto a freshly-erased volume, then use Migration Assistant to migrate data from the CCC backup. A bootable volume is not required for this procedure.
Using Migration Assistant to restore your startup disk from a CCC backup