Late 2015 iMac doesn't boot and Disk Util shows Fusion HDD as "uninitialized"

[sebalvarez]

Well, today is a horrible day. My trusty iMac, which never gave me a problem since I bought it in 2016 (late 2015 model) booted up to the circle with the line across. I booted into recovery, launched disk utility, and I couldn't believe what I was seeing because it didn't make any sense. This iMac has a 3 TB Fusion drive with the SSD being 128 GB. Disk Utility was showing me that the main drive was 4.14 GB, which doesn't make any sense. Just in case I made a Monterey bootable USB stick in my MacBook Pro and booted from it, but same thing. You can see a photo of it below.

I know that mechanical drives can fail pretty fast, but up until last night, it gave me no indication, and last time I ran a first aid on it was a few days ago and it was fine. And I don't know if diagnostics mode checks for drive problems, but I booted into it and told me everything was OK.

I don't know if maybe I was hacked, but in those cases usually they don't ruin your drive, they encrypt your drive and demand a ransom, which hasn't happened.

I'm not going to take it to an Apple Store, I have a Mac Studio coming in June, and I have my MacBook Pro in the meantime. At most, I would spend around $300 in the cheapest macsales.com replacement SSD and kit so I can still use it until I get the Mac Studio.

Has anyone seen this behavior? Does the fact that it shows 4.14 GB as the HDD mean that it is toast and the files can't be recovered? Or is this some kind of logical error with the boot table or something like that?

Basically I would like to know if there’s any way I can recover my files, all the local folders that are not automatically uploaded to iCloud.

 

[rm5]

Fusion Drives are known to fail pretty regularly, and spontaneously in your case. In fact, last December, four iMacs in one of my school computer labs had to be repaired/wiped because the FDs failed.

Do you have a backup you can restore macOS from? Because I believe you'll have to erase everything in the process and reinstall macOS.

Try going View > Show All Devices, and erasing the whole disk (one at the VERY TOP).

If that doesn't work, try out the diskutil resetFusion command in Terminal (in recovery obviously). Details here: https://support.apple.com/en-us/HT207584

And if this doesn't work after multiple attempts, you might have to replace the drive.

Hope this helps.

 

[Fishrrman]

My suggestions:

Don't open this iMac.

Instead, get an external USB SSD.
Set up the SSD to be an external boot drive. (easy to do on a Mac)
Now you can get up-and-running again.
(It doesn't absolutely have to be an SSD. If you have a spare platter-based HDD around, even that should work. But an SSD is the better choice.)

Once up-and-running, see if you can access the internal fusion drive.
May or may NOT be possible, but you really need to get fully booted to get a better handle on the situation.
But you can't get "fully booted" unless you have "an alternative boot source" -- that's why you need the external boot drive.

It looks like something got corrupted on the hard drive portion of the fusion drive.
Could be software.
Could be hardware.
If it's a hardware failure, you're probably not getting any of the data back.

 

[sebalvarez]

Yeah, it's probably a hardware failure. I did install macOS to an external Samsung T5 1 TB SSD, but it was a pain in the ass. I created a bootable installer to a new Sandisk thumb drive, ran a diskpart clean command on the T5 on my PC to erase it and be able to format as GPT in Disk Utility. Then connected the installer thumb drive and the T5 to the iMac, booted from the installer, formatted it as APFS GPT, and it would go all the way to 18 mins left and then reboot, and back to showing the Apple logo with 29 mins left all the way to 18 and over and over. So after an hour I decided it was long enough and forced shutdown.

Then I repeated this process in my Macbook Pro and it installed fine to the T5. When it finished installing I didn't do all the steps, I shut down the Macbook Pro and connected the T5 to the iMac. It worked fine, until it gave me a kernel panic of which the first line is:

panic(cpu 0 caller 0xffffff801e02c081): AppleAHCIDiskQueueManager::setPowerState(0xffffff8b8a498240 : 0xffffff801ff7fcf0, 3 -> 0) timed out after 100259 ms @IOServicePM.cpp:5524

And then a bunch of other stuff and a long list of kexts.

Thinking it might be something wrong with this installation, I did the whole process all over again, but it still happens on the second installation. I tried to do a diskutil resetfusion and it also gave me errors, so the Fusion SSD is fine, but obviously the HDD is not, because it shows that it's 4.14 GB. The big problem is that I'm fine using the iMac with the OS on the T5, but not if it's going to keep crashing without warning, then it's useless. In that case, I would have to either buy the full kit from macsales and open it up (which I've seen the videos and I really dread the prospect of doing that, plus spending over $300 to save a machine that, while I love, I do have a very expensive Mac Studio coming in two months, so this iMac is not a machine that I would like to spend any money in. However, since I paid $3,000 for it, I would like to keep it in working order.

So yeah, the external SSD solution is great, the problem is, the damn HDD keeps crashing the system. Is there a way to prevent that?

 

[Fishrrman]

Not sure why you did the things you did as explained in reply 4 above.

Why don't you try it THIS way?

1. Have iMac powered off. Connect the external drive which is to become the external BOOT drive.

2. Boot to INTERNET recovery:
Command-OPTION-R
at boot

3. If you are using wifi, you need your wifi password. The internet utilities take a while to load, be patient.

4. Once the internet utilities load, open disk utility.

5. VERY IMPORTANT: if there is a "view" menu, go to it and choose SHOW ALL DEVICES.

6. Select the external drive, then erase it to:
a. APFS, GUID partition format (if you are using Mojave or later)
b. Mac OS extended with journaling enabled, GUID partition format (High Sierra or earlier)

7. When done, quit disk utility and open the OS installer.

8. Start clicking through. When the installer asks WHERE you want to install, "point it" at the EXTERNAL drive, and continue.

9. The Mac will reboot one or more times and the screen may go dark for a minute or more with no other indication of activity. Be patient.

10. When done, you should see the initial startup screen (choose your language). Start "clicking through". Set up a VERY BASIC account. All you need is a username and password. Don't bother with anything else.

11. At this point, you should be able to get "booted to the finder" from the external drive. Can you do that?

 

[DeltaMac]

Your internal hard drive (HDD) may continue to cause problems - it's still connected, even if you choose to not use it now.
The best way out of that situation is to physically disconnect the internal hard drive, which means opening up your iMac.

 

[sebalvarez]

Not sure why you did the things you did as explained in reply 4 above.

Why don't you try it THIS way?

1. Have iMac powered off. Connect the external drive which is to become the external BOOT drive.

2. Boot to INTERNET recovery:
Command-OPTION-R
at boot

3. If you are using wifi, you need your wifi password. The internet utilities take a while to load, be patient.

4. Once the internet utilities load, open disk utility.

5. VERY IMPORTANT: if there is a "view" menu, go to it and choose SHOW ALL DEVICES.

6. Select the external drive, then erase it to:
a. APFS, GUID partition format (if you are using Mojave or later)
b. Mac OS extended with journaling enabled, GUID partition format (High Sierra or earlier)

7. When done, quit disk utility and open the OS installer.

8. Start clicking through. When the installer asks WHERE you want to install, "point it" at the EXTERNAL drive, and continue.

9. The Mac will reboot one or more times and the screen may go dark for a minute or more with no other indication of activity. Be patient.

10. When done, you should see the initial startup screen (choose your language). Start "clicking through". Set up a VERY BASIC account. All you need is a username and password. Don't bother with anything else.

11. At this point, you should be able to get "booted to the finder" from the external drive. Can you do that?

Sorry, I'm not sure what you mean by "Not sure why you did the things you did as explained in reply 4 above." The point is to still use the iMac, but with the external SSD as the boot drive. So the steps I took are more or less what you described here, except that I didn't boot into internet recovery because I had made a bootable USB thumb drive with the latest macOS Monterey installer, so no point in waiting for internet recovery, the USB installer achieves the same purpose. But I didn't setup a basic account, I setup my normal account because it's my main computer and I hope it's going to be for a while, but I want to try to find a solution to the kernel panic thing, because I would hate to have to spend money in the kit to open it up just to disconnect the Fusion drive.

 

[sebalvarez]

Your internal hard drive (HDD) may continue to cause problems - it's still connected, even if you choose to not use it now.
The best way out of that situation is to physically disconnect the internal hard drive, which means opening up your iMac.

This is the first time I see something like this in any computer, Mac or PC. I've had lots of HDDs fail over the years, but when failing, it would simply not work, but that didn't impact the computer in any way, much less a kernel panic.

 

[DeltaMac]

Keep in mind that the fusion drive is not one device. It is two devices, the hard drive, and an SSD card.
If you continue getting the crashes, the problem will often be the hard drive. It's just dying, and that's one of the symptoms. There is a terminal command that might bypass the hard drive - but sometimes that does not fix the crashes because the hard drive is still connected, so continues to get power. The fix then is to remove (or just unplug) the device - the hard drive. The SSD card is probably not affecting anything, even if it might be bad. AND, then you have to decide if you really want to make your iMac work better, and that means that you have to open the iMac, and disconnect (or remove) the bad hard drive. THAT is not too bad, just some tricky stuff removing all the tape residue, and re-taping for the reassembly. If you find that you have to remove the SSD, that's a lot more time, and you end up removing most of the parts inside your iMac because the SSD card is on the back of the logic board, which has to be removed to get to the SSD slot.
I don't think you will need to do anything with the SSD, just the hard drive. Look at the steps that are involved in getting to the hard drive. iFixit.com has good steps for that. You can decide if that's something that you want to do...

iMac Intel 27" Retina 5K Display Hard Drive Replacement

Follow this guide to replace the hard drive for your iMac. Replacing the hard drive requires separating the display and moving the left speaker....

www.ifixit.com

 

[sebalvarez]

There is a terminal command that might bypass the hard drive

Thanks, I would like to give that a try before I have to disassemble the machine. What's that command?

 

[DeltaMac]

You caught me -- I did not wish to give you the idea that I know what that command is. I have never had a need for that, but I recall reading threads here related to disabling an internal drive, probably using ioreg or maybe diskutil.
I do remember that it didn't always help, and is a system/bus configuration command that must be entered correctly. That much I remember...
I did search around today for the threads that mentioned disabling a hard drive. I did not have a lot of luck, and not with your exact needs (disabling an internal drive)

 

[sebalvarez]

No problem, but I'll keep searching for it just in case. Thanks anyway.

 

[sebalvarez]

I guess a good question for people with far more knowledge than me would be, is there a way to prevent loading the SATA kext at bootup? Or even the Intel 10 chip that handles it. Because in this computer, the only use for SATA was for that drive, which is now broken, so maybe if there's a way to prevent the SATA Intel 10 chip driver or kext from loading, that's all it takes. Maybe, just a logical thing to question which may not be possible at all.

 

[sebalvarez]

I think I'm going to post that question in a new thread along with the complete kernel panic log, this thread became too long for anyone to really follow.