External drive boots Monterey as an installer, but not as a "regular" startup disc

Question

Level 1

10 points

External drive boots Monterey as an installer, but not as a "regular" startup disc

I have external USB 2TB magnetic drive that boots my 2015 Intel Mac fine as an installer (with Option key, GUID partition map, Monterey 12.7.5), but I'd like to boot from it as a regular, everyday Mac. It is not seen as a possible startup disk.

I have an M2 at my disposal, but it is going in the shop. I want to use this external as "personal Mac" while my M2 is away and I don't want to mess with the log-in IDs that are working perfectly well when booting from the internal SSD.

I suppose I can easily make a new log-in, but I'd like to know what I need to do to make this drive act as a typical boot disk.

Thanks.

Posted on Jun 8, 2024 4:05 PM

Reply

Answer 1

Top-ranking reply

HWTech

Community+ 2026

Level 9

71,946 points

Jun 9, 2024 5:45 PM in response to Mark3324

It is best to use a USB stick for the installer. Yes, it is possible to use a single hard drive for both the macOS installer and the full macOS installation (I have personally done this with macOS Ventura & Sonoma). However, you need to have a separate partition for each one. The partition for the full OS installation needs to be APFS (top option).

When you erased the external drive, did you erase the whole physical drive or just the existing volume? It is best to erase the whole physical drive in order to create a new partition table since drives from the factory may include some odd hidden partitions or other oddities that could affect some operating systems. See this Apple article for details since Disk Utility with macOS 10.13+ now defaults to hiding the physical drives from view by default:

Erase and reformat a storage device in Disk Utility on Mac - Apple Support

The destination volume for the full OS installation needs to be at least 100GB+ just for the base OS installation.....more storage is needed depending on the apps & data that will be stored on it. At least 20GB+ of Free storage space is always required for the normal operation of macOS (more depending on the workload).

Macs can be very picky about the drives used for booting. So there is a possibility the external drive may not be compatible.

Make sure to disconnect all other external devices in case one of them is causing a problem. Also, connect the external drive directly to the Mac.

Reply

Answer 2

Mark3324 Author

Level 1

10 points

Jun 9, 2024 8:49 AM in response to BDAqua

I do own CCC (yes, a real license!). They have a good article at bootable backups at https://bombich.com/en/kb/ccc/6/cloning-macos-system-volumes-apple-software-restore so I will make one using the Recovery method or the tips at CCC. I thought CCC could not make a bootable copy at all.

Reply

Answer 3

Jun 9, 2024 1:02 AM in response to Mark3324

Maybe the external drive was prepared as macOS installer? You could try to erase it and install "real" macOS on it. ...and maybe use Migration Assistant to copy the internal disk data to it in case it is erased in the service? Or do you already have a backup of the internal disk?

Reply

Answer 4

BDAqua

Level 10

250,719 points

Jun 9, 2024 8:04 AM in response to Mark3324

I'd use Carbon Copy Cloner Legacy Mode to accomplish it...

http://www.bombich.com/software/ccc.html

Reply

Answer 5

Mark3324 Author

Level 1

10 points

Jun 9, 2024 8:55 AM in response to Matti Haveri

Yes, the bootable drive was created as a step of creating an installer drive from the steps at Create a bootable installer for macOS - Apple Support. I don't bother with a backup of the old Mac -- it sits off to the side as something I might need on rare occasion.

Reply

Answer 6

Jun 9, 2024 8:54 AM in response to BDAqua

I'd use Carbon Copy Cloner Legacy Mode to accomplish it...

I was about to recommend that, but cloning Silicon Macs might not be as successful as doing a regular install and then migrating, so I recommended the latter.

Reply