2019 27" iMac won't boot up - In Disk Utility it's telling me I cannot re-install Sonoma because there's suddenly only 14GB of HD space!

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2019 27" iMac won't boot up - In Disk Utility it's telling me I cannot re-install Sonoma because there's suddenly only 14GB of HD space!

Hi

My iMac began behaving strangely today, wouldn't open any software (mostly Adobe Creative Cloud apps) or sync with my Work's Open Drive...

I tried to restart the Mac, but now it keeps stalling when the progress bar is about halfway across, every time.

Eventually I booted up in recovery mode - first Aid in disk Utility found no problems. I concluded it might be a good idea to re-install Sonoma (it's been pestering to update to the latest version for a few days now anyway) but that's when it informed me there wasn't enough HD space to do that - only 14GB free from a 1TB Hard drive... there should be in excess of 170+GB free at my last reckoning. I'm assuming something is log-jamming somewhere but I can't access it to clear it. Can anyone help please, as I won't be able to continue working if i don't solve it.

Many thanks

Simon

iMac (2017 – 2020)

Posted on Jul 12, 2024 9:54 AM

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Answer 1

Top-ranking reply

Tesserax

Level 10

158,712 points

Jul 12, 2024 11:26 AM in response to Simon@afterimage

Actually those two volumes are "normal" for a Mac running macOS Sonoma. What rkaufmann87 is referring to is that some Mac models were equipped with a Fusion Drive. This drive actually consists of two physical drives: a smaller SSD & a larger capacity HDD. When working normally, they appear as a single drive. In any case, it is possible for these Fusion drives to become "split." That is, they no longer function as a single entity, but as two separate drives ... and quite possibly why you are only seeing this 14GB of space.

Ref: About Fusion Drive, a storage option for some Mac computers - Apple Support

As such, once you verify that your Mac has a Fusion drive, you can use this support article to restore it:

How to fix a split Fusion Drive - Apple Support

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Answer 2

Jul 12, 2024 10:04 AM in response to Simon@afterimage

You need to go to disk Util in recovery mode and fully erase the disk (Typically named Macintosh HD)to the APFS format and then try to re install it Note please have a backup of your disk before fully erasing it.

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Answer 3

rkaufmann87

Level 10

148,624 points

Jul 12, 2024 10:47 AM in response to Simon@afterimage

I would hazard to guess the computer has a Fusion Drive and the drive is split. You need to research that before trying to move forward!

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Answer 4

Tesserax

Level 10

158,712 points

Jul 13, 2024 8:46 AM in response to Simon@afterimage

Yes, it appears that your Mac's Fusion Drive in intact.

For erasing and reinstalling macOS:

Use Disk Utility to erase an Intel-based Mac - Apple Support
How to ‘clean’ install modern macOS - Apple Support

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Answer 5

Jul 12, 2024 10:48 AM in response to rkaufmann87

Hi

the Macintosh HD has 2 volumes: Macintosh HD and Macintosh HD - Data (in fact, when I ran the First Aid over the 'Data' volume it has shown up quite a few issues...

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Answer 6

Jul 12, 2024 10:16 AM in response to Fjordservers

Thank you for your quick reply.

In Disk Utility, can I go straight to restoring from my Time Machine Backup, or will I have to Erase the disk first?

Just wondering if using "Restore from Time Machine" will achieve the same thing without Erasing in Utility first?

Thanks

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Answer 7

Jul 13, 2024 1:17 AM in response to Tesserax

Hi

apologies - I had to split away from this overnight…

thanks for the info so far . What I’ve done is click “view all devices” and it does look like I have a Fusion Drive.

I have taken a photo of the fusion info, as well as the info of the HD and HD-Data volumes…

from looking at these does it indicate I would be correct to fix the Fusion Drive? (Sorry these are appearing upside down on my screen - no idea why, ha!)

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Answer 8

Jul 13, 2024 1:47 AM in response to Tesserax

UPDATE...., Since I sent the images, I have read that if I can see a fully labelled Fusion Drive (as I can here) this means my fusion drive is working - is this correct? - therefore is it possible I can proceed to Fjordservers suggestion of erasing and re-installing from my Time Machine? Thanks :-)

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2019 27" iMac won't boot up - In Disk Utility it's telling me I cannot re-install Sonoma because there's suddenly only 14GB of HD space!

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