Help with making a bootable drive

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Help with making a bootable drive

Hi Apple Community, tearing what is left of my hair out and hoping that you can help me with creating a bootable external Big Sur drive.

Background: My internal Fusion Drive is unusable. It shows up and accepts data (I did get it to load Big Sur but it runs at a glacial pace.) I have now erased it.

I then successfully installed Big Sur onto a 3TB external HDD connected via Thunderbolt. This has been running well ever since I installed it a couple of weeks ago.

However it is noisy and I want to get better speed, so I bought a 2TB Crucial SSD and my plan is to migrate everything over to this drive and make it my Start Up drive.

Problems (There are a few!)

The main problem is that NONE of my keyboard start-up commands work. Cmd R, Opt Cmd R, Opt, I can’t even start up in Safe Boot using Shift.

I have used a keyboard checker and all keys and key combinations are working fine.

So every time the Mac starts up, it goes directly to the Big Sur startup screen on my Thunderbolt drive, no matter what keys I hold down.

This means that I can’t get the Big Sur Installer to complete its installation onto the 2TB SSD, because as soon as it gets to the Restart part of the process, the Mac just reverts to starting up from the Thunderbolt drive.

I have used Carbon Copy Cloner to copy the Thunderbolt Data Volume across to the SSD, and I have downloaded the Big Sur installer into my Applications folder on the Thunderbolt drive so theoretically when I use the installer to install Big Sur onto the SSD, that should make it bootable. 😳

I know that the lack of a working internal drive makes this a very non standard problem, but I am hoping there is someone out there who wouldn’t mind helping me troubleshoot shoot this.

iMac 27″, macOS 11.0

Posted on Nov 28, 2020 4:50 AM

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Answer 1

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humphrey_g Author

Level 1

10 points

Nov 29, 2020 9:18 AM in response to putnik

Thank you Putnik, your steer led me to the solution! Just in case anyone else faces this problem, here is what I discovered:

Using Terminal to make the bootable USB Big Sur Installer was critical. (Note: It takes _much_ longer than you would think to complete, in my case around 90 minutes to do the last step - just be patient the progress does eventually get to 100%)
However, as before, none of my keyboard start-up commands worked, so I was unable to choose the USB as my start-up. (Note that even selecting a start-up drive in Preferences also wouldn't work!)
My suspicion was that my bad internal drive, which kept mounting, was somehow preventing the keyboard start up commands, so the next step was to find a way to prevent my internal drive from mounting and I found this https://apple.stackexchange.com/questions/236105/prevent-internal-drive-from-mounting-automatically
As soon as the internal drive stopped mounting, my keyboard start up commands started working again and so I was able to successfully use the USB to install Big Sur on my 2TB SSD which I was _then_ able to choose as my start-up!

I have NO idea why the Internal drive was screwing things up, but hopefully this ghost in the machine is now put to rest and I can enjoy a faster Big Sur on my external SSD driving my Driveless iMac.

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Answer 2

putnik

Level 4

1,179 points

Nov 28, 2020 5:38 AM in response to humphrey_g

This might help. (I did a simple internet search for it.) You'll need a slightly larger USB for the 12Gb Big Sur installer. I use 32Gb formatted HFS+.

https://support.apple.com/en-us/HT201372

The Firmware should still give you boot options (Alt key at startup). So I would disconnect the present system and boot to the USB or clone, with a copy of the installer on it. Then carry out some disk checks and reformatting before installing on the SSD. Any attempt to run on an HDD is incredibly slow and futile.

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Help with making a bootable drive

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