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Boot iMac from external SSD

Help, I have read that a great way to speed up my 2014 iMac is to boot from an external SSD. I have formatted the drive as directed and used Carbon Copy cloner and restarted holding down the option key but it does not recognise the drive as bootable. What am I doing wrong?

iMac 21.5″, macOS 11.1

Posted on Aug 30, 2021 1:48 PM

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Question marked as Top-ranking reply

Posted on Aug 30, 2021 2:11 PM

when i set up an external startup drive for big sur, i didn't use a bootable clone. i did a clean install of the macOS on the external drive and then manually moved the things i wanted onto the external drive. to set it up, i started out by using the instructions in the well written user tip supplied below.


How to Setup and Use an External SSD as your Startup Disk - User Tip


now, when i want to boot into the external, i hold the option key on startup until i see the screen where i choose which drive i want. or if you are going to exclusively use the external drive, set it as your startup disk in SystemPreferences > StartupDisk

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Question marked as Top-ranking reply

Aug 30, 2021 2:11 PM in response to Jack of Hearts

when i set up an external startup drive for big sur, i didn't use a bootable clone. i did a clean install of the macOS on the external drive and then manually moved the things i wanted onto the external drive. to set it up, i started out by using the instructions in the well written user tip supplied below.


How to Setup and Use an External SSD as your Startup Disk - User Tip


now, when i want to boot into the external, i hold the option key on startup until i see the screen where i choose which drive i want. or if you are going to exclusively use the external drive, set it as your startup disk in SystemPreferences > StartupDisk

Aug 30, 2021 4:52 PM in response to Jack of Hearts

Once you erase the entire disk and format it as the following:



you'll need to setup CCC as shown, Control (right) - click on the destination drive and select "Legacy Bootable Backup Assistant…" from the contextual menu.



Then click Start in the next window. This takes less than about ⅓ the time it takes to do a fresh install and migrate from the original boot drive or Time Machine with Migration Assistant.


Boot iMac from external SSD

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