How to install external Thunderbolt 3 SSD to use as startup drive for iMac 2019

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gobears1990 Author

Level 1

9 points

How to install external Thunderbolt 3 SSD to use as startup drive for iMac 2019

Hello~ I have been suffering with an extremely slow hard drive for months, probably years. I finally got serious with etrecheck and it suggests using an external Thunderbolt 3 SSD drive for the startup drive. I have purchased that and am ready to move forward.

My question is, how do I load the OS there, and once I've done that, how do I start up from that disk in the future?

Thanks so much - I've googled everything I can think of & can't find solid info. Attaching the report for reference. PS. I do have my info backed up.

Etre check report - disk drive failing

iMac 21.5″, macOS 12.3

Posted on Mar 20, 2022 8:58 AM

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Answer 1

gobears1990 Author

Level 1

9 points

Mar 21, 2022 3:41 PM in response to gobears1990

This was super helpful, from EtreSoft:

Try the instructions from this web site instead: https://www.chriswrites.com/how-to-run-any-version-of-macos-from-an-external-hard-drive/

You can download the full installer from Monterey from Apple: How to upgrade to macOS Monterey - Apple Support

Then you can just run the “Install macOS Monterey” app that will be installed in your Applications folder.

The only trick is that you will need to select your external drive as the target of the installation.

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Answer 2

Ronasara

Level 6

14,703 points

Mar 21, 2022 11:27 AM in response to gobears1990

The other alternative to Carbon copy Cloner, if you do not have it, is to follow the steps below.

First be sure that the new external disk to be used is properly formatted the same as your HD is.
Connect the external disk to your Mac with an Ethernet cable. I recommend that you do not do the download via Wi-Fi. It's too slow for these large files and will usually fail.
Go to the Apple App Store.
Enter the name of your computer's current operating system under Search. You will then be given a download link.
Click on it and let it do the download. This may take up to an hour, more or less.
When the download is complete you will be presented with a window to start the installation of the operating system. It will ask you where to install it. Select the external disk and click Install.
The installation can also take up to an hour, ore or less, with several automatic restarts.
When done you can open System Preferences and select the new disk as your startup disk.

You should find that this will increase your computer's speed by up to 50%.

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Answer 3

tbirdvet

Level 6

13,893 points

Mar 20, 2022 1:39 PM in response to gobears1990

I have a 2019 iMac. Your model has a very slow drive and not much memory to run Monterey. I used Carbon Copy Cloner to make an external drive and made it bootable (you need to specify that) and it works fine. An external SSD will help the speed. However, you may want to consider a newer Mac down the road.

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Answer 4

Mar 21, 2022 12:27 PM in response to gobears1990

How to set the Startup Disk

your new drive will appear as an option above when it has the OS installed on it.

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Answer 5

gobears1990 Author

Level 1

9 points

Mar 21, 2022 3:39 PM in response to Glen Doggett

Thank you so much - I had never noticed that!

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How to install external Thunderbolt 3 SSD to use as startup drive for iMac 2019

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