How do I make an external SSD Bootable

ronaldfromsunset valley wrote:

I have a 27" 2020 iMac running Monterey 12.3.1I would like to make a new external SSD bootable? So far I've used CCC6 to make a copy of my present system but it's not bootable. The internal Drive , 500gig, is getting full. I wish I would have bought this iMac with a 1 TB drive. oh well.

Q - " So far I've used CCC6 to make a copy of my present system but it's not bootable. "

A - Think one ( you ) will find CCC Developer does not suggest attempting to make a Bootable Clone on Monterey 12.3.1 and above.

Apple has implemented some addition changes in 12.3.1 and above making the ASR function an even more " Best Effort "

https://bombich.com/kb/ccc6/macos-monterey-known-issues

https://bombich.com/kb/ccc6/frequently-asked-questions-about-ccc-and-macos-11

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

You maybe better off Installing Monterey Directly to the External SSD Drive only if the Internal Drive is a Rotational / Mechanical or Fusion Drive. Otherwise there would be very little performance gains

ronaldfromsunset valley wrote:

Internal is SSD External is SSD I would like to boot from the external.

See my post above. In recent macs, you have to go through hoops in order to allow external booting.

About Startup Security Utility on a Mac with the Apple T2 Security Chip - Apple Support

Two things:

1) in order to be able to boot your mac from an external drive, you need to first restart in Recovery Mode, run Startup Security Utility and change the settings to the middle or low level.

2) If your internal drive is an HD or a Fusion Drive, then by all means boot from an external SSD if possible. If your internal is an SSD, then it is best to boot from it, and offload some of your data to the external.

You are welcome and thank you too.

Do come back to the Apple Support Communities ( ASC )  in the future, if / or when additional questions may arise

Be an empty external to quickest port on Mac port on it! Depends is the SSD,NVME or a traditional hard drive?

I made an external SSD using CCC but trying to boot with it was slow and at times locked up the Mac so now just make data backups. For your external SSD format to APFS GUID partition.