how do you set up an external ssd as the startup disk
iMac 21.5″, macOS 10.13
Yes. What system are you using now?
Also I'd use Carbon Copy Cloner
If you have trouble with CCC you can create a bootable flash drive according to this document and boot into it and select the SSD to install on: How to create a bootable installer for macOS - Apple Support
So...if I clone my current hard drive to the external drive, it would appear as a choice in the startup disk preference pane?
Then, I would select it to be the startup disk; click restart and we would have liftoff?
I'm on Catalina 10.15.7 (the last/latest version)
I have CCC
Now, I have to get the new external HD - looking at LaCie rugged Pro 2TB
anticipate using it just for the OS and Apps; all documents, photo files, etc
on other external hds.
I strongly recommend one of the OWC SSDs. They are by far the more reliable available and have the best customer support I've run across. Look at these: OWC Envoy Pro EX . Check with customer support to see which type will give your iMac model the fastest speed.
If it has a bootable system on it you would do it in the System/Startup Disk preference pane:
I will definitely check them out - THANKS AGAIN!!!
how do you set up an external hard drive as the startup disk for imac 21.5" retina 4k, 2017
