You can make a difference in the Apple Support Community!

When you sign up with your Apple Account, you can provide valuable feedback to other community members by upvoting helpful replies and User Tips.

Looks like no one’s replied in a while. To start the conversation again, simply ask a new question.

Mac Pro running Catalina cannot recognize other bootable external volumes at startup (left option)

Greetings,

My 2013 Mac Pro has lost its ability to mount external boot volumes. The issue could be the Mac Pro, or it could be that the other OS volume has some sort of corruption with startup files, but, here's the scenario:

The Mac Pro is running Catalina. The external drive has a fully functional High Sierra installed on it and will easily mount in another older Mac Pro, appearing to be healthy and fine. It is connected to the Catalina Mac Pro via Thunderbolt 2.

1) When I start up pressing the <left option> key, the startup menu only recognizes the Catalina volume.

2) If, in Catalina, I go the "Startup Disk" Preference pane, it sees both volumes (Catalina and High Sierra) - I can select High Sierra is a startup volume. However, on subsequent boot up, that volume is not seen and the Mac reverts to booting up in its "native" OS of Catalina.


All was well until a few days ago, now I have this issue.

Any advice or direction would be much appreciated.

Thank you,

dncollins

Mac Pro, 10.15

Posted on Sep 3, 2021 3:32 PM

Reply
Question marked as Top-ranking reply

Posted on Sep 3, 2021 5:45 PM

Hmmm, start with these...


Have you done a PRAM reset, CMD+Option+p+r...


http://support.apple.com/kb/HT1379


In fact, do 3 in a row, takes a bit of time.


Intel-based Macs: Resetting the System Management Controller (SMC)...


http://support.apple.com/kb/HT3964

Similar questions

8 replies

Sep 5, 2021 12:29 PM in response to BDAqua

That's my thought.....am scouring for the correct command to use in Terminal, but not sure how to verbalize the issue for a correct search. "Mac Pro not recognizing external boot volumes at Left-Option startup" isn't eliciting any relevant responses. I have considered taking the missing volume (High Sierra) and refreshing the OS on it via Recovery Mode, but I would have to do that on the old Mac Pro - doing so has yielded a firmware issue on <that> machine that I am working through - a sort of parallel issue to this one :-\


DC

Mac Pro running Catalina cannot recognize other bootable external volumes at startup (left option)

Welcome to Apple Support Community
A forum where Apple customers help each other with their products. Get started with your Apple Account.