Issue with external startup disk being bypassed by the native drive. (iMac - macOS Catalina)

[iSuedhead]

I'm not sure if this is in the right section, but here goes:

Background:
I've been running (macOS Catalina) on a late 2013 iMac from an external startup drive (860 EVO - 1tb) and had to do a clean install after running into an issue with Filevault, where my keyboard and mouse would stop working after a reboot. I was basically forced to do a clean install because I couldn't disable Filevault for some reason.

Never had an issue with this setup before this FileVault issue started happening.

Issue:
After doing a complete wipe of the above mentioned drive and a clean install of Catalina, I ran into a very particular issue I never encountered before: if other USB-drives are hooked up to the iMac, it boots up (on reboot) with the native hybrid drive (macOS Mojave) instead of the external SSD. For some reason other externals make the startup process bypass the external startup drive. I double checked in system preferences and the external SSD is selected as the default startup drive.

Sure I can disconnect all the externals before rebooting, but that doesn't fix the problem. And it is kinda annoying since the iMac is mostly used as a Plex server.

I'm wondering if the name of the startup disk could be an issue?

Things I've tried so far:
Reinstall Catalina to the external drive (3 times)
Tried different cases (2) and cables (5) for the external drive

Anyone have an idea what's going on? And how I would be able to fix this?

 

[grafiksol]

I have two suggestions you might try. No guarantees, but probably worth trying...

Suggestion 1
Assume you are aware of the 'Option key during startup' technique to allow selection of available startup drives (regardless of System Preference setting)? Using that technique (with the USB drives connected) does the external SSD appear in the resulting list of available startup drives? If so, select the SSD as the startup volume and let the startup process continue. Once the machine is up and running from the SSD, restart again (no Option key) and see if the SSD remains the boot volume.

Suggestion 2
Using the 'Terminal' application (two assumptions, first that you are familiar with Terminal and second that the 'Root' user is enabled)
Boot the iMac using the internal Mojave drive (with the USB drives connected). Launch the Terminal application, then key in the following:

sudo bless -mount /Volumes/[SSD Volume Name] -setBoot. (hit 'Return' on the keyboard, and enter Root user password when prompted. Note that if SSD volume name includes a space, put quotes around the name when entering the command, ie "SSD External")
shutdown -r now (hit 'Return' on the keyboard)

The iMac should reboot from the external SSD drive. Once the startup process is complete, restart again and see if the SSD remains the startup drive.



If you are managing this iMac remotely (or have the ability to) the above commands can be put into a short script that can be executed remotely to restart the machine using the desired startup volume. And happy to post such a script.

 

[mdgm]

If that doesn't resolve it you may also want to try resetting the NVRAM.

 

[grafiksol]

Indeed. "mdgm" is on the ball, and I should have suggested that first. A simple process to implement which may immediately fix the problem. Thanks mdgm!!

 

[brianmowrey]

OP issue seems to be the same as many are experiencing just a few threads over after the December security update.

 

[mdgm]

In that thread a SMC reset resolved it for at least one user

 

[iSuedhead]

I tried all the above, nothing seems to fix the issue. Except disconnecting the other externals. I reset SMC & NVRAM. I tried the terminal thing, but I got 'error'-message. Someone posted that the issue seems tied to a security update, maybe I should just do another clean install of Catalina and skip the latest security update? Seems worth trying.

That said, thank you all for chiming in! I really appreciate it.