Using an external SSD as my startup disk with my Mac mini

I seem to be in the same boat, only with my Late 2104 Mac mini. I have two systems. An M1 2020 MacBook Pro running Monterey 12.6.2, which I can boot from an external drive thanks to the OWC Envoy Express (https://eshop.macsales.com/item/OWC/TB3ENVXP00/). For the Mac min I have tried everything listed in this Community with no luck. In the (Use an external SSD as your startup disk … - Apple Community) page it does state the the drive needs to be a true Apple HD. In my Mac mini the drive is an Apple PCI Express, so maybe that's the issue. In any event, it's very frustrating for those of us that have grown comfortable with the whole "clone" emergency disk.

When you clone using CCC you need to designate it to be bootable using the "legacy" feature. If you just clone it will not be bootable.

https://bombich.com/kb/ccc6/cloning-macos-system-volumes-apple-software-restore

After trying for several weeks and 6 hours of phone conferences with Apple techs, and being unable to reliably create a bootable external SSD backup drive (Samsung 870 EVO in each case), I came across two articles indicating that there is little need to create such a drive. First, an Apple silicon Mac (M1, M2 chip series) will not boot up from any such external SSD if its internal drive has failed!! Not knowing this cost me time, money, and a LOT of frustration. However, it is documented at https://tidbits.com/2021/05/27/an-m1-mac-cant-boot-from-an-external-drive-if-its-internal-drive-is-dead/ and at https://bombich.com/kb/ccc6/cloning-macos-system-volumes-apple-software-restore (somewhat buried, but mentioned twice in the latter article). Further, while pre-Ventura OS may allow creating such bootable backups, Ventura makes it darned near impossible with its Systems Integrity Protection (SIP) system (which seems to make things worse with every OS upgrade). It is bad enough that while I managed to create a bootable backup with Ventura 13.0.1, it won't even let me upgrade to 13.1, even if I boot up with it.

I was able to create both Monterey and Ventura bootable installation drives - Monterey on a thumb drive and Ventura on an external rotating platter HD. Being a nut for backups, I do have my data backed up on two external SSDs via both Carbon Copy Cloner and by Time machine. At least, if my Mac Mini M1 internal SSD fails (which requires replacement of the motherboard), I will be able to restore my data and my OS settings after restoring the OS on the replacement internal drive from either of the OS installation drives. Having that ability negates the need for bootable external drives for the M1.

[Edited by Moderator] 

Hi,

Just wonder if you did resetting NVRAM which could solve your issue.

Reset NVRAM on your Mac - Apple Support

Also if I were you, I would replace internal HDD with SSD which you copied by CCC.

If this is an Apple Silicon M1 Mini, they can be very fussy in terms of which external drives are actually bootable reliably.

Generally, Thunderbolt drives tend to the most reliable at making bootable drives via cloning or a direct install. When it comes to USB based drives it seems to be a tossup as to which ones will work and sometimes given a specific drive and manufacturer, they may boot on one M1 Mac but not another.

Also note that later versions of macOS and M1s, may not reliably clone and and be bootable and CCC, SuperDuper, etc. also state as such. Also, are you sure when you clone that in CCC at least, you are selecting legacy clone? If not, it will only clone the data volume which is defiantly not bootable.

In all cases, the drive also need to be directly connected to the Mac and cannot have any sort of hub in between.

Hi,

Try to make bootable clone drive with Carbon Copy Cloner, select source drive ,internal drive, destination drive external drive then start to make clone.

https://bombich.com/

> the external SSD never shows up in the Startup Disk panel

Does it not show with Option-boot either?

"Mac Mini (late 2014) running on Monterrey 12.6.1 "

Not an M1. Simply not possible.