Install mac os on an external SSD drive

Welcome to Apple Support Communities.

Unfortunately, there is a current server issue on Apple's side for the How to get old versions of macOS - Apple Support downloads. I would try again later. However, when the servers work again, you can make a macOS Catalina bootable installer (How to create a bootable installer for macOS - Apple Support), boot with it, and install onto the external SSD and follow the User Tip.

Also, what external SSD are you using?

Jack

Just to be clear. an update is when a newer version of the same operating system is installed. An upgrade is when a newer operating system is installed such as upgrading from Big Sur to Monterey. They are completely different things. Your problem may be that the external disk needs to first be reformatted the same as your HD is. Try that and a link for Catalina is below. Also, be sure to use Safari to access it. Firefox likely will not work. Good luck.

 Catalina

TimORourkie wrote:

I have been attempting to install OS on a Samsung external ssd on my 2017 iMac to make it my boot drive and, in general, full replacement for the native drive. Managed to go into disk utility to reformat the SSD. Can not find a way back into disk utility to download the OS. After which, I'd like to restore from Time Machine. Absolutely no help from Apple. Chat not available. Did they all go home? Frustrated. Not happy. I cannot imagine that a whole bunch of people would want to make this entirely sensible upgrade. Why, oh why, is it so hard to get this done?

Follow these steps: How to Setup and Use an External SSD as y… - Apple Community. Also, I would not recommend using a Samsung SSD. If you are in the return period, I would follow the current recommendations found in the User Tip.

What was the exact error? Does it work if you Start up your Mac in safe mode - Apple Support?

Jack

In my experience, I have found these to be more reliable:

• G-Technology 2TB G-DRIVE mobile SSD R-Series Storage - Apple
• SanDisk Professional G-DRIVE SSD - Western Digital

Though, I hope the Samsung works for you.

Jack

I have been attempting to install OS on a Samsung external ssd on my 2017 iMac to make it my boot drive and, in general, full replacement for the native drive. Managed to go into disk utility to reformat the SSD. Can not find a way back into disk utility to download the OS. After which, I'd like to restore from Time Machine. Absolutely no help from Apple. Chat not available. Did they all go home? Frustrated. Not happy. I cannot imagine that a whole bunch of people would want to make this entirely sensible upgrade. Why, oh why, is it so hard to get this done?

Thanks for the lightening fast reply and excellent documentation. Followed the instructions. Updated the OS on the original drive to Monterey. Formatted the SSD specifying APFS, GUID. Clicked the link to load Monterey (again, this time to the SSD). Was careful to select the correct drive (again). Looked fine for awhile. Then I got an error about a problem with the download. Did a rinse and repeat on the format and download. Got the same result.

I called the drive SanDisk SSD rather than MacIntosh HD. I gather that is fine, as YouTube tutorials show people using a name other than MacIntosh HD for their boot drive.

Restarted the iMac and repeated the format and download. Same result.

So, I'm guessing the next instruction I need to follow is "I would not recommend using a Samsung SSD". Dang. Am in return window, so all I'm losing is time. But at my age . . .

Thanks again. In particular, for the time you save me.

I can't recall the exact error. Something along the lines of operation couldn't complete. Not real specific.

I went through 2 or 3 iterations of erasing the drive and attempting to install the OS. Every install failed. A couple of the erase attempts failed. I tried a couple of different instructions on the erase. I.e., you suggested APFS, which I used a few times. I also tried a scheme that was recommended elsewhere. I shut down the iMac. I unplugged the drive. I swapped cables. Nothing worked.

And then we got into the Twilight Zone. I looked at information on the drive in Disk Utility. Characteristics included Writeable: no, Available space: 0, Purgeable space: 0, Can be verified: no, Can be repaired no, Journaled: no. Not real encouraging.

I had my son plug the drive into his home built 'gamer' pc to see if it was a compatibility issue. His pc didn't see the drive. But then he got a message that there was a power surge on one of his ports. Other weird stuff happened. Yanked the drive and rebooted.

I looked at the drive you recommended. On the plus side, per the specs, it's very fast. Also, I can throw it out of my second story window, bounce it off cement into a 3 foot tall rain barrel, leave it in there for 30 minutes, fish it out, and park my car on it. Impressive. But I don't need a drive that fast. It's also kind of spendy, at around $700. I just need to store bunch of music and photos. So, am hoping for a 2 tb drive more in the $300-350 range. I'm surprised these SSDs aren't more compatible.

I might contact Western Digital on Monday, or I might just send it back. I'm guessing I received faulty hardware. However, to avoid another round of extensive troubleshooting, I'm hoping to find out what would be a reasonably priced drive that is compatible and reasonably reliable.

YouTube made it look so easy.

Thanks again for your help with this. No one should have to walk this road alone.