Using Samsung T7 SSD as a bootable drive

Hello Community,


I am having trouble formatting my SSD to use as a bootable drive. I've done everything right to erase, rename, select GUID Partition Map and format to APFS.


However, when I reboot the mac and attempt to run the installation of the OS, it says :

"This volume is not formatted as APFS"


So then I erase and retry all these steps again, open Terminal and run the script and it says:

"APFS disks may not be used as bootable install media" - and then it fails to erase.


Why is it so hard? What am I doing wrong?

Mac mini, macOS 12.1

Posted on Oct 9, 2022 5:34 AM

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Question marked as Top-ranking reply

Posted on Oct 11, 2022 7:55 AM

Here is how you should go about installing the OS on an external drive:


1) Get yourself a USB3 thumb drive - it must be at least 16GB, probably better 32GB


2) Dowload the installer from the App Store. If it starts after downloading, quit the installer.


3) Follow the instructions here to make a bootable installer on the thumb drive:


How to create a bootable installer for macOS - Apple Support


4) Start your mac, and hold down Option key (in an intel mac) or keep pressing and holding the power button (Apple Silicon mac)

Choose to boot from the installer drive


5) Run Disk Utility from the installer, and erase the SSD - the whole drive, not just the volumes in it - as APFS with GUID


6) Quit Disk Utility and start the installation, choosing the SSD as your target drive.


7) (optional) when the installation is done, migrate the user accounts from the internal drive (do not migrate anything else; instead install fresh copies of your applications)

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24 replies

Oct 11, 2022 8:51 AM in response to michawilson

michawilson wrote:

it was my belief that the fuller the storage, the slower the drive.

With modern computers, the opposite is sometimes true. A 500 GB SSD is sometimes implemented as two 250 GB chips. The system can read from both chips simultaneously and do so twice as fast as it can read from one.

In saying this, the computer is not slow at all (yet), however I do still have to sort out the issue of the teeny storage capacity.. Therefore I thought having a 1TB SSD as the start-up disk would be great as I'd be able to keep all my files arranged as is, rather than having half here, half there.

I strongly recommend the half here, half there approach. You should be able to identify those documents that you really haven't used in 6 years. Those are the ones to put on the external drive.


Another possible solution would be iCloud Drive. Go to Apple ID > iCloud > iCloud Drive and make sure that "Desktop and Documents" is checked and "Optimize Mac Storage" is checked. This will cost some money, but is a really easy way to make 2 TB of storage available on a 256 GB hard drive.

I factory reset the old imac and it's quicker than it was, but still slower than the brand newie.. Would it be possible to install Monterey (or another OS) onto the SSD from that computer and use it as its main drive? (for speed purposes).

You can definitely use the SSD as a boot drive on the old computer. I often recommend that to people who have older iMacs that are difficult to upgrade.


One issue to remember. If you do go all in to iCloud, make sure that your old computer has the same settings but with "Optimize Mac Storage" turned off. That will make sure that all of your iCloud data is downloaded to the machine with more storage available. Then, when you backup the iMac, it will backup your iCloud data too.


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Using Samsung T7 SSD as a bootable drive

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