iMAC 27 i7 steadfast refusal to complete bootup

Question

iMAC 27 i7 steadfast refusal to complete bootup

Hello everyone.

I have an i7 27-inch iMAC from 2013. Of late I have had difficulty booting the machine up and it has now completely refused to do so. The Apple logo screen appears and the progress bar goes all the way to the end then........stays there. I have tried all the usual diagnostics, re-installing MAC OS, etc. Every test gives the unit a hearty "thumbs up" claiming no problems exist!

One clue I have found is this. When I boot in Verbose mode, I get an error telling me that Disk 2S1 has an i/o error. usually the sign of a failed disk. however, when I run Disk utility there is a list of Disks as follows:

MAC OS Base System Disk 1S1

Macintosh HD Disk 3S5

MacIntosh HD Data Disk 3S1

There is no mention of the 2S1 disk which Verbose mode reports as having an i/o error! (I have included a screenshot of the mythical disk).

This maybe a red herring but it is the only thing I can think of to follow as a lead.

The machine in question has a 3TB Fusion drive, OS 10.15.7 and 32GB RAM.

Any help out there?

Many thanks,

Eddie

iMac 27″, macOS 10.15

Posted on May 24, 2023 3:59 AM

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Answer 1

Top-ranking reply

D.I. Johnson

Level 8

43,267 points

May 30, 2023 6:19 AM in response to Eddie in Prestwick

Okay, so this Terminal list looks pretty normal. Your disk2s1 is a normal partition of the boot drive. It is usually hidden unless the computer is booted in Recovery mode, at which time is allows access to some OS functions. Nothing unusual here.

In your case, there may be an issue with the data on that partition that is effecting the startup and hanging the machine.

Reboot again in Recovery and launch Disk Utility. Click View > Show All Devices in Disk Utility. Does ** identify your startup drive as Fusion drive? It should.

If ** doesn't identify a Fusion drive, then you'll need to fix that.

Please see: How to fix a split Fusion Drive - Apple Support

Please post a screenshot of the ** display for each device so that we can get a look at what you see.

Run the Disk Utility First Aid routines on the startup drive device(s) and each volume or partition indented below it. Do this until ** reports no errors, it should not take more than a couple passes.

If errors persist, then I would would suggest to erase and reformat the drive and reinstall macOS once again.

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Answer 2

May 24, 2023 4:26 AM in response to Eddie in Prestwick

I believe you are correct that the I/O error is indicative of a drive failure.

How did you manage to reinstall macOS and/or run drive diagnostics? Does this iMac boot into Recovery mode?

Have you attempted to boot into Safe mode (press and hold the shift key down at startup)? It can take much longer to safe boot (5 min) so be patient.

How to use safe mode on your Mac - Apple Support

If you have access to another Mac that can run macOS Catalina, try installing Catalina on an external drive and see if you can boot the troublesome iMac from that.

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Answer 3

BDAqua

Level 10

251,419 points

May 30, 2023 5:43 AM in response to Eddie in Prestwick

ls1 & ls2 are just determined by load order.of the drives/partitions.

You can use Drive DX to possibly get a better view of Drive health…

https://binaryfruit.com/drivedx

Thanks to Jack-19…

It may be wise to run SMART Utility to check the drives' health.

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Answer 4

May 26, 2023 12:48 PM in response to Eddie in Prestwick

To be clear, booting into Safe mode could take 10 minutes or more, so if you have not given the Mac fifteen minutes to boot, try that again.

Also, since Disk Utility does not seem to indicate the presence fo disk2s1, let's see what the Terminal app can tell us.

Disconnect any exter

Launch Terminal, and then enter this text on the command line: diskutil list

Then press Enter.

The result should look something like this:

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Answer 5

May 26, 2023 10:21 AM in response to D.I. Johnson

Thanks for the replay and helpful suggestions. Apologies for the delay in replying but I wanted to make sure I had all the answers to your questions.

Yes, it boots up into recovery and I can run Disk Utility, re-install MAC OS, etc with no hassles. The only time it goes wrong is when I re-boot and it sticks at the end of the progress bar.

It will not boot into safe mode ( even with great patience and encouraging words. It just sits at the end of the progress bar defiantly refusing to go any further.

I do have a MacBook from a similar year and will try to external drive install you suggest.

Do you have any thoughts as to why the i/o error is showing on a disk that Disk Utility doesn't list?

Eddie

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Answer 6

May 30, 2023 5:07 AM in response to D.I. Johnson

I finally managed to get some time to create a bootable USB and re-install 10.15.7 to see if that helped. It did not. I then ran terminal as suggested and, for reasons I don't understand, 2S1 is now showing as the 2GB MAC OS Base System - which was previously listed as 1S1. Screenshot of current status attached. I can only assume that the re-installation of 10.15.7 somehow changed this as am 100% certain of the fact that 1S1 was correct and that 2S1 was not listed until today.

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Answer 7

Jun 5, 2023 7:01 AM in response to D.I. Johnson

Thanks again for taking time to review my issues. ** did identify as Fusion. I have attached 6 screenshots (1-6) showing the all devices view. I then tried to run First Aid but got error messages - additional attached screenshots (7-16). I then tried to erase and format but got a final error message and was unable to do anything after this. I have tried to reboot but am now faced with a blinking white folder icon with a black question mark. I believe this is because the machine can't find a suitable startup disk with the OS. If I try to boot into recovery it asks me to chose a network but the input is so slow - literally minutes to input the password for the network - and nothing happens when I click the continue arrow. In essence, as of this moment, I am stuck on the "choose network" Recovery screen.

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iMAC 27 i7 steadfast refusal to complete bootup

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