iMac restarts on shutdown and then displays flashing question mark

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iMac restarts on shutdown and then displays flashing question mark

I boot my iMac from an external 2TB SSD (by Crucial) because the internal Fusion drive no longer functions correctly. I have been running Big Sur without problem for a few weeks but now when I choose 'shutdown' everything appears to close down gracefully and then it immediately restarts and displays the flashing question mark screen. The only way I can restart is to choose OPT when I press the power button and then choose the 2TB SSD, whereupon it boots normally.

I followed the sequence suggested in support.apple.com (What to do when you get the flashing question mark) up to and including reinstalling Big Sur from Recovery onto the SSD. Note: Even during the installation process, every time the Installer would re-start it went to flashing question mark, and the only way that I could complete the installation was to do a power button restart + Opt and then select the Installer.

I have included below the EtreCheck report which suggests no major errors.

My feeling is that somehow the bad internal drive (which I have wiped) is overriding the normal start-up. I found a Terminal routine which prevents it from mounting and showing up on the desktop, but maybe there are more steps I need to take to make sure that this is not causing my problems.

Any help and advice is most gratefully received. This iMac has a beautiful 27inch 5K screen and except for the bad internal drive is my perfect Home Office desktop computer.

Humphrey

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EtreCheck Report Attached

EtreCheck Report

iMac 27″, 11.0

Posted on Dec 9, 2020 6:51 AM

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Answer 1

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den.thed

Level 10

81,742 points

Dec 9, 2020 9:56 AM in response to humphrey_g

Hmm... maybe try splitting up the Fusion drive first.

see > https://www.lifewire.com/split-fusion-drive-apart-2260166

and > https://www.easymacsupport.com/blog/split-apple-fusion-drive-in-catalina-mojave-and-build-fusion-again

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Answer 2

den.thed

Level 10

81,742 points

Dec 9, 2020 8:59 AM in response to humphrey_g

Does this happen with the external IcyBox drives disconnected at startup?

(test a startup cycle with just the 2T external startup disk connected)

Did this start yesterday on 2020-12-8 after the macOS Big Sur 11.0.1 update?

(that update may have fix somethings and broke others)

Have you tried just sleeping the iMac, instead of fully shutting it down?

(unlike PC's, Mac's can sleep for days or even weeks without restarting)

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Answer 3

humphrey_g Author

Level 1

10 points

Dec 9, 2020 9:40 AM in response to rkaufmann87

Hi @rkaufmann87,

Thanks for your reply to my dilemma.

Yes, I set up the SSD to be my bootable drive, and it is so specified in System Preferences. And I have checked it multiple times, to make sure it hadn't somehow got changed. When I can get Power On + Opt to work (it takes multiple attempts) then it shows the SSD and boots normally.

Could you comment on the possibility that somehow there is something associated to the bad internal (Fusion) drive that is interrupting the start up? I have tried to split apart the internal SSD from the spinny HD, but the Terminal process I am using keeps telling me that there are no Logical Core Storage Groups available, and I need this Identifier to split them apart. I know that the SSD bit is fine. This internal drive tests OK via Disk Utility, and I was able to install Big Sur, but it took a VERY long time, and it ran incredibly slowly (minutes between command and result). So I wiped it and used another Terminal process to stop it from mounting.

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Answer 4

humphrey_g Author

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Dec 9, 2020 9:53 AM in response to den.thed

Hi there and many thanks for your suggestions. I had the Mac on a scheduled daily shutdown, but since this happened, I have suspended any shutdown and am just leaving it on 24/7. In my testing, I have found that Power On + Opt does not always work, and it seems to take many attempts to bring up the screen with the start up choices (otherwise it just brings up the flashing question mark).

Right now I am reluctant to shut it down because of the difficulty in getting it to respond to OPT at Start up and this is my main Work-From-Home computer, so I haven't yet tried with the IcyBox drives disconnected (I use these to store my media files). I am crossing my fingers that someone will reply with a definitive solution, so I don't have to play Russian roulette with the Start Up. 🤞

In answer to your question about the 11.0.1 Update, this was the one that I used to set up the SSD with originally as I think that update came in quite quickly after the initial release. It had been shutting down and starting up normally until 6 Dec when this problem began.

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Answer 5

humphrey_g Author

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10 points

Dec 12, 2020 1:41 AM in response to den.thed

HUGE THANK YOU! This has solved my problem (Recap: My internal Fusion Drive is bad. I migrated everything to an external 2TB SSD made bootable with Big Sur, but on restart machine went automatically to Flashing Question Mark. Only recourse was to boot with OPT and then select the 2TB SSD which then booted normally.)

I felt quite sure that, although I had wiped the internal drive, something was interrupting the start-up process and preventing the 2TB SSD from mounting. I wanted to split apart the internal Fusion drive, but the only method I had found was the lifewire one and this didn't work for me. HOWEVER, your second suggestion from easymacsupport DID work, and now my machine boots normally (and quickly) from the external 2TB SSD!

The engineer in me would love to know how the 'ghost in my machine' was creating this grief, but I am just happy that this problem has now gone away. I know that my late 2014 iMac will eventually be too old for OS updates, but in the meantime I will get as many years out of it as I can because I love its 5K 27inch display.

Thank you again!

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