How to make external drive my iMac Mojave startup

My internal drive is failing and cannot update OS from Mojave to Catalina using internal hd. So I have some external drives I want to select one from and make my startup. One is single SSD and other is regular hd. I know how to format either but what are my options on installing the OS? internet Recovery then when booting choose the external drive or is there easier way

Posted on Nov 30, 2019 10:55 AM

1 reply

Kappy

Level 10 (363,125 points)

Nov 30, 2019 11:35 AM in response to starbux48

The SSD would be the better choice. If you need to do Internet Recovery then do this:

Internet/Network Recovery of El Capitan or Later on a Clean Disk

If possible back up your files before proceeding.

Restart the computer. Immediately after the chime hold down the (Command-Option-R) keys until a globe appears.
The Utility Menu will appear in from 5-20 minutes. Be patient.
Select Disk Utility and click on the Continue button.
When Disk Utility loads select the target drive (will be the out-dented entry) from the side list.
Click on the Erase button in Disk Utility's toolbar. A panel will drop down.
Set the partition scheme to GUID.
Set the Format type to APFS (SSDs only) or Mac OS Extended (Journaled.)
Click on the Apply button, then click on the Done button when it activates.
Quit Disk Utility and return to the Utility Menu.
Select Install OS X and click on the Continue button.