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Big Sur on an external SSD

I have a 21" Mac (2016) which was always awfully slow; and then I went and upgraded to Big Sur. To try and make it smoother I want to install and boot Big Sur from an external SSD. I have a new T1 Samsung drive. Looking for a link/instructions.

Would be grateful for any advice and suggestions...web search did not get me very far.

Thank you

iMac 21.5″, macOS 11.0

Posted on Jan 6, 2021 5:33 AM

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Question marked as Top-ranking reply

Posted on Jan 6, 2021 6:36 AM

You can use your current macOS installation to do it.


First go to the Mac App Store and download Big Sur installation here https://itunes.apple.com/br/app/macos-big-sur/id1526878132?ls=1&mt=12 . This will prompt you the update interface and ask you to download the Big Sur installer. Click download and it will create a "Install macOS Big Sur.app" in the Applications folder and automatically launch the installer when download is finished. Close it for now.

Plug the SSD to the Mac, Open Disk Utility, Locate the external disk and format it APFS How to erase your Intel-based Mac - Apple Support (NOTE: forget the instruction to enter Recovery Mode, you don't need it now, only open Disk Utility and use it as indicated in this article to format the external drive). Here's some more detailed information on Disk Utility Erase and reformat a storage device in Disk Utility on Mac - Apple Support

Once the external disk is formatted, go to Applications folder, launch the macOS installer you downloaded and follow the instruction.

Attention to choose the correct drive right in the beginning, pointing the installation to the external drive.


Once installed, you'll have to restart holding Option and select the external disk.


With this method you'll always have to pay attention to the USB connection because it can easily disconnect if you move your Mac, the SSD or even if the desk is shaken or vibrates somehow, you know. You'll have to guarantee they're always well connected.

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15 replies
Question marked as Top-ranking reply

Jan 6, 2021 6:36 AM in response to crr100

You can use your current macOS installation to do it.


First go to the Mac App Store and download Big Sur installation here https://itunes.apple.com/br/app/macos-big-sur/id1526878132?ls=1&mt=12 . This will prompt you the update interface and ask you to download the Big Sur installer. Click download and it will create a "Install macOS Big Sur.app" in the Applications folder and automatically launch the installer when download is finished. Close it for now.

Plug the SSD to the Mac, Open Disk Utility, Locate the external disk and format it APFS How to erase your Intel-based Mac - Apple Support (NOTE: forget the instruction to enter Recovery Mode, you don't need it now, only open Disk Utility and use it as indicated in this article to format the external drive). Here's some more detailed information on Disk Utility Erase and reformat a storage device in Disk Utility on Mac - Apple Support

Once the external disk is formatted, go to Applications folder, launch the macOS installer you downloaded and follow the instruction.

Attention to choose the correct drive right in the beginning, pointing the installation to the external drive.


Once installed, you'll have to restart holding Option and select the external disk.


With this method you'll always have to pay attention to the USB connection because it can easily disconnect if you move your Mac, the SSD or even if the desk is shaken or vibrates somehow, you know. You'll have to guarantee they're always well connected.

Jan 6, 2021 7:34 AM in response to Rafael Scheid

If I may, have seen numerous issues attempting to do the same thing in Catalina and people have had unsolved issue after the Catalina Security Update 2020-01. Was working with this and they never had a foolproof solution. Yesterday, was working with another person attempting the Big Sur on iMac 2014 on External Drive. Same issue in Catalina appeared in Big Sur. Sure, they could install Big Sur to external drive but no matter what they did, even going into Startup Disk as Admin Account and changing to external drive - No way would Big Sur boot to External Drive @ Startup.


This does not mean it will not work for you but . . . ?

Jan 17, 2021 2:08 AM in response to Rafael Scheid

Just to let you and @P. Philips know that I managed with a bit of an effort to install Big Sur 11.1 on the SSD. it is working beautifully now. Thank you.


Of course, I must watch out for what may happen during an upgrade of Big Sur 11.1


(The effort was that since 11.0.1 was already on the Mac, I couldn't download 11.1 as an installation file -- it automatically upgrades. Solved the problem by downloading a .pkg file and working from there.)


Hugely relieved...I have suffered a groaning Mac for close to 5 years -- in an attempt to save money I got a slow moving ox. But not any more


Big Sur on an external SSD

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