Trouble Fixing Split Fusion Drive

[my12by60]

I bought a 2017 imac 27 on ebay in used condition. My job has me working on the internet. So I like the big screen and speed of the machine. This imac has a 28gb start up drive (I presume SSD) and 1TB HDD. I keep getting the disk almost full notice. So I did some reading here and see that I am only using the 28gb SSD. The HDD seems to be stranded with nothing saving to it. The machine is running Mojave.

I read about the diskutil resetFusion command in terminal and tried to unite the two drives. But that failed and I got these results. Any ideas on what to try next would be appreciated. Thank you.

 

[Fishrrman]

I'll offer another possible solution.

You have a 2017 iMac which has USBc ports that should support USB3.1 gen2 speeds (up to 1,000MBps).

Get an nvme blade SSD (size is up to you, I reckon 512gb minimum).
Get a USB3.1 gen2 enclosure (many available).
Snap them together and set this up to become your new, EXTERNAL boot SSD.

Move the contents of the internal SSD over using CarbonCopyCloner, which is FREE to download and use for 30 days -- doing it "my way" costs you nothing.

Now, boot and run from the external USB3.1 gen2 drive.
I predict you'll be very pleased with the performance you get from it.

Alternative:
Samsung and Sandisk (and others) sell "pre-packaged, ready-to-use" USB3.1 gen2 drives, such as the t7, Sandisk Extreme, etc.
But it's nearly as easy to "build your own"...

 

[Weaselboy]

How to fix a split Fusion Drive - Apple Support

If your Fusion Drive appears as two drives instead of one in the Finder, it's no longer working as a Fusion Drive. Here's how to fix it.

support.apple.com

I think the problem there is you are booted to macOS and not in recovery. Try holding command-r at boot to get to recovery, then run the command in Terminal.

 

[my12by60]

Fish - Thanks for the ideas on the external SSD. Before I go that route, I would like to see how the machine works with original fusion drive working properly.

Weasel - I had tried diskutil resetFusion in both macOS and recovery and got very similar results. I just tried recovery mode again and got the attached results.

 

[chrfr]

Fish - Thanks for the ideas on the external SSD. Before I go that route, I would like to see how the machine works with original fusion drive working properly.

Weasel - I had tried diskutil resetFusion in both macOS and recovery and got very similar results. I just tried recovery mode again and got the attached results.View attachment 1795739View attachment 1795741BoView attachment 1795741

Boot from Internet Recovery, not regular recovery. If you open Disk Utility, the app may offer to repair this for you after you erase both disks. Otherwise, try again to reset the Fusion Drive once you've erased each one.

 

[my12by60]

Sorry, I am a novice at this activity. How do I boot from Internet Recovery vs. regular recovery?

 

[allan.nyholm]

what if you just format both the drives

 

[chrfr]

Sorry, I am a novice at this activity. How do I boot from Internet Recovery vs. regular recovery?

Command-option-r at startup instead of command-r.

 

[allan.nyholm]

you can make a fusion drive after the fact after both drives have been formatted.. try 'diskutil apfs deletecontainer disk3'

if you have stuff on the drives the above command takes care of deleting that too.

 

[my12by60]

Not sure of the order of events being recommended.

Should I boot into Internet Recovery mode then try the command that allan has suggested?

 

[allan.nyholm]

you should boot off a USB key with a modern macOS on - like Big Sur or Catalina -- Or use Shift-Option-Command+R for Internet recovery which should get you access to the macOS that came with your iMac

If that version is not cabable of controlling APFS formatted drives and able to do what I propose then return.. and I bet someone can help.. My best guess is that you will get a macOS version that can handle APFS and use my above command to split the APFS drive for good and allow you to either make a new fusion drive or do without .

 

[my12by60]

My machine is running Mojave.

 

[allan.nyholm]

My machine is running Mojave.

you would need to get off the recovery partition on your current drive - defunct or not. The internet recovery method would be good. You wouldn't be able to delete or modify your drives off the partition that hold the recovery - usually the rotational drive in this case. I have a 2015 iMac that didn't come with a fusion drive built in - so I might be wrong on where the recovery partition lies; ssd or hdd.

I think Mojave has the apfs command too attached to diskutil

I bet someone more clever than me can answer you better

 

[chrfr]

Not sure of the order of events being recommended.

Should I boot into Internet Recovery mode then try the command that allan has suggested?

Just start up from Internet Recovery, and try disk utility first as I'd already suggested. The disks can't be reconfigured as required if you're running from regular recovery. Then if Disk Utility doesn't work, then try the reset Fusion command you were already doing.
Also, be sure you've disconnected any external drives from the computer at the time you're trying to do this.

 

[taphil]

I just went through this with a 2015 iMac to trade in. I had to use Option-Command-R to initiate the latest version of MacOS and internet recovery.

Reboot iMac.
When you hear chime, hit Option-Command-R.
Enter wifi password if needed or plug in Ethernet cable
iMac will download Big Sur internet recovery.
Open Disk Utility. Click on View All Devices and verify you have both SSD and HDD.
Erase the SSD (format as GUID and APFS)
Erase the HDD (format as GUID and APFS)
Quit Disk Utility
Open Terminal and type diskutil resetFusion
Quit Terminal.
(I rebooted at this point, don't know if needed, and pressed Option-Command-R to start Big Sur Internet Recovery again.)
Install Big Sur.

 

[my12by60]

Just start up from Internet Recovery, and try disk utility first as I'd already suggested. The disks can't be reconfigured as required if you're running from regular recovery. Then if Disk Utility doesn't work, then try the reset Fusion command you were already doing.
Also, be sure you've disconnected any external drives from the computer at the time you're trying to do this.

Sorry I have been gone. I went with this advice from chrf and did the following:

- boot from Internet Recovery
- use Disk Utility to erase both disks (the iMac was calling these two disks Start Up and HDD0
- get back to Terminal and type in resetFusion
- respond with Yes when asked

Now I'm back up and running with Big Sur instead of Mojave. Looks like I have to rebuild some things like my preferred dock set-up and some favorites. But otherwise the machine seems to be working well.

Thanks for all of the help up to this point.

 

[my12by60]

Ok. Time Machine backups have been loaded and the machine is working fast and nice. No sign of any data or file losses. I never would have figured this out on my own. So thanks again to the forum for the big assist. My imac is up and running, the Suns beat the Clips, Rahm (ex-ASU Sun Devil) won the US Open, and the kids are taking me out for sushi dinner. Life is good.

 

[allan.nyholm]

@my12by60 congratulations on having your iMac up and running - and I apologize for leading you astray

I hope you had a good night out.

 

[my12by60]

No worries Allan. I think multiple suggestions in the thread would have worked. The advice from chrfr was just the easiest for me to follow and execute.