Installing Catalina on external hard disk

[garreto]

Hi all,
I have had an older version of the IMac (21.5-inch, late 2012) for a while now. Because the internal disk had become extremely slow, I successfully switched to using an external USB hard disk (a Seagate).

This has worked great so far, but now I am trying to update from OS 10.14.13 (Mojave) to 10.15 (Catalina) and am unable to do so. When I try to install the new OS it says "the volume is not formatted as APFS".

I have attempted to erase the external disk, reformat with APFS and then restore the latest time machine backup, but nothing. Likely when it restores the back up it goes back to non-APFS because I am still unable to install Catalina.

I'd be glad for any pointer/suggestion for updating my Mac.

Thank you.

Gar

 

[Fishrrman]

"I am trying to update from OS 10.14.13 (Mojave) to 10.15 (Catalina) and am unable to do so. When I try to install the new OS it says "the volume is not formatted as APFS". "

That's because you have to re-format the external drive to APFS (with GUID partition map) BEFORE you can install Catalina.

BUT... I WOULD NOT try to install Catalina on a "platter-based" external drive.
An SSD... ok (I've done that myself).
But it's going to run poorly if you install to a platter-based drive.

What version of the OS are you using now...?

 

[NewUsername]

You should get an external SSD. Samsung T7 would be perfect for this.

Then, boot up with option-command-R, go to disk utility, click View -> Show all devices, reformat ("erase") the drive as APFS and GUID partition scheme, and then install macOS.

 

[garreto]

Thanks all. I do have a SSD (it's a seagate). I'll try to research this GUID partition scheme thing.
At the moment it is running Mojave.

 

[joevt]

Create a new partition for Catalina (use a new disk or shrink the Mojave partition), then after Catalina is installed, use Migration Assistant to get your files, apps, and settings from Mojave.

 

[garreto]

I actually tried to do that, but once installed Catalina the backups done with time machine were not visible anymore from my IMac. I could only migrate from the backups done on my laptop which has Catalina as well.