Startup problem with external ssd drives turned on

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Level 1

4 points

Startup problem with external ssd drives turned on

I have a brand spankin' new iMac i9 with a 2TB SSD internal drive. I have 2 external SSDs connected via Thunderbolt; these drives contain only audio and video files. Here's the (to me at least) strange behavior:

I shut down the iMac. If I turn on the external drives and then power up the iMac I get the flashing question mark. If the external drives remain off the iMac starts normally. Restarting presents no difficulties regardless of whether the external drives are on or not.

Yes, I'm aware: If I just leave the hard drives turned off until the iMac powers up there will be no problem. What I'm really asking, though, is whether anyone thinks this could point to a hardware problem within the iMac. It seems odd that it can't find the startup system simply because the externals are powered up and connected. The startup disk program in system preferences shows only the internal ssd, as it should.

Seems bizarre to me. Any thoughts? I have AppleCare.

Jim

iMac i9, 10.15.4

iMac 27", macOS 10.12

Posted on Mar 30, 2020 2:55 PM

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Answer 1

Top-ranking reply

BDAqua

Level 10

244,817 points

Mar 30, 2020 4:15 PM in response to Stone162

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

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Answer 2

HWTech

Level 9

59,960 points

Mar 30, 2020 5:52 PM in response to Stone162

Try running the Apple Diagnostics.

It is hard to say whether this indicates a potential problem with the iMac or if it is just some odd compatibility issue with your external Thunderbolt drives. I've seen a lot of odd Mac behavior recently so it would not surprise me this is just some compatibility issue.

FYI, don't forget to reselect your Startup Disk after resetting the PRAM.

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Answer 3

Stone162 Author

Level 1

4 points

Mar 30, 2020 3:52 PM in response to BDAqua

Thanks so much for the reply.

That's right. The Startup Disk pane says "You have chosen 'Untitled 10.15.4' as your startup disk."

I just tried it again--same thing. At first the glowing white apple appears, the external drives blink for 30 seconds, then I ge the question mark. If I turn the drives off the iMac starts up as normal.

The externals are powered via the Thunderbolt cable, if you think that might make a difference.

Jim

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Answer 4

Stone162 Author

Level 1

4 points

Mar 30, 2020 5:41 PM in response to BDAqua

I did the PRAM reset three times. Aside from the screen going momentarily blank there was no obvious indication that a change had occurred (this iMac has no chime at startup). So I'm not entirely sure I accomplished anything there. Anyway, I did that 3 times and did the SMC reset, but the odd behavior persists. Before I did any of this I made sure that Startup Disk in System Prefs had my internal SSD chosen.

Again, the behavior of the computer aside from this seems to be ok. Maybe I just need to eject and power down the external SSDs as a rule, which I probably should be doing anyway. So long as this isn't an indication of a more general hardware problem, I'll work with it.

Jim

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Answer 5

Stone162 Author

Level 1

4 points

Mar 30, 2020 5:58 PM in response to HWTech

I did check and the internal ssd was chosen. I'd already run the hardware diagnostics test and that came up empty.

Since no one has chimed in with "Me too!" I'll figure this could be an oddity with these two drives. I may connect another drive from a different manufacturer and different interface just to see what happens. I'll report back in the hopes that it may help someone else.

Thanks to both of you for the suggestions.

Jim

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