Some Macs, especially those produced prior to 2014, cannot "see" the content of a volume that lies past the 2TB mark on the disk at boot. Some Macs may not boot from USB devices larger than 2TB If CCC's Task Plan didn't report any configuration concerns for your backup volume and you are having trouble booting from it, try the Firmware Discoverability Troubleshooting steps below. Ordinarily, a CCC bootable backup volume will appear in this list, but occasionally your Mac's firmware may have difficulty discovering the hardware that hosts your backup. Using only device drivers that are stored on your Mac's firmware chip, the firmware will scan all of your SATA, PCI, USB, and Thunderbolt busses for hard drive devices, then read those hard drive volume headers to determine if a macOS system is available on each volume. When you boot your Mac while holding down the Option key, the Mac Startup Manager will display a list of available startup devices. Sometimes the Mac's firmware cannot detect your backup device Cloning macOS System volumes with Apple Software Restore.Some Big Sur startup volumes don’t appear in the Startup Disk Preference Pane.If that does not produce a bootable device, then the device is not suitable for functioning as a bootable device on your Mac. If that does not produce a bootable volume, and if you have exhausted the Firmware Discoverability Troubleshooting steps below, then we recommend that you install macOS onto the backup.
When you make a backup of a Big Sur startup disk with CCC 5.1.23 or later, CCC will automatically use Apple's proprietary APFS replication utility (ASR) to make an exact copy of the source. 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. Starting in macOS Big Sur, the system now resides on a "Signed System Volume". MacOS 11, "Big Sur" bootability troubleshooting
If you're trying to migrate content to a new Mac, use Migration Assistant for that purpose - do not attempt to restore an older Mac's backup onto a new Mac. No Mac will ever boot from an OS that is older than what it shipped withĪpple has never supported booting a new Mac from an OS that is older than what it shipped with. If you're having trouble with the steps or have run out of options, please let us know how far you got, or how far your Mac gets into the boot process.
Before you ask for help, please try the troubleshooting steps below. We're happy to help you troubleshoot your bootability problems.
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