How to fix my split Fusion Drive (iMac) using Mojave

[lawful]

I've tried Apple explanation and it didn't work: https://support.apple.com/en-us/HT207584

My mistake was to erase all volumes with Disk Utility to perform a fresh install and now I don't know how to fix muy Fusion Drive. Thank in advance for reading my post and for your time.

 

[casperes1996]

My mistake was to erase all volumes with Disk Utility to perform a fresh install and now I don't know how to fix muy Fusion Drive. Thank in advance for reading my post and for your time.

You say you've followed Apple's instructions - what went wrong in that process?
Please post the output of diskutil list

Beware that re-fusing will erase all data.

 

[lawful]

You say you've followed Apple's instructions - what went wrong in that process?
Please post the output of diskutil list

Beware that re-fusing will erase all data.

Thank you for your help

 

[casperes1996]

Please also post the output of diskutil list

 

[priitv8]

I used these instructions to create my own fusion drive on my Mac Mini.
So if you are doing it from scratch (you'll lose your data, as said above), you can follow these:
https://blog.macsales.com/36227-everything-you-need-to-create-your-own-fusion-drive/
Alternative discussions on the same topic:
https://www.lifewire.com/setting-up-fusion-drive-mac-2260165
https://forums.macrumors.com/threads/diy-fusion-drive.2147511/

 

[lawful]

I used these instructions to create my own fusion drive on my Mac Mini.
So if you are doing it from scratch (you'll lose your data, as said above), you can follow these:
https://blog.macsales.com/36227-everything-you-need-to-create-your-own-fusion-drive/
Alternative discussions on the same topic:
https://www.lifewire.com/setting-up-fusion-drive-mac-2260165
https://forums.macrumors.com/threads/diy-fusion-drive.2147511/

Thank you for your answer.

 

[casperes1996]

Thank you for your answer.

The issue with the reset command. Was that it was seeing too many drives and didn’t know which to use.

 

[lawful]

The issue with the reset command. Was that it was seeing too many drives and didn’t know which to use.

Ok thank you and how do I solve it?

 

[casperes1996]

Ok thank you and how do I solve it?

As requested, send output of diskutil list and I will instruct further.

 

[lawful]

As requested, send output of diskutil list and I will instruct further.

 

[casperes1996]

Run the following commands in order. If you get an error, stop, and post it.

diskutil ap deleteContainer disk2
diskutil ap createContainer -main disk0 -secondary disk1

You've now created an APFS container fusing the drives. We aren't quite done though, cause there's no volume in the container
Run diskutil list again, and locate the one named "synthesised". In your last screenshot it was disk3, but it may have changed now - that's why you need to run and check again. Then run

diskutil ap addVolume disk# APFS [name of new drive]
replacing # by the number of the synthesised disk and [name of new drive] with the name you'd like for the volume. If you want spaces in the name, but it in quotes "".

 

[lawful]

Run the following commands in order. If you get an error, stop, and post it.

diskutil ap deleteContainer disk2
diskutil ap createContainer -main disk0 -secondary disk1

You've now created an APFS container fusing the drives. We aren't quite done though, cause there's no volume in the container
Run diskutil list again, and locate the one named "synthesised". In your last screenshot it was disk3, but it may have changed now - that's why you need to run and check again. Then run

diskutil ap addVolume disk# APFS [name of new drive]
replacing # by the number of the synthesised disk and [name of new drive] with the name you'd like for the volume. If you want spaces in the name, but it in quotes "".

I did already solve it!! Thank you very much

 

[casperes1996]

I did already solve it!! Thank you very much

Good to hear. You're welcome anyway .

 

[lawful]

Good to hear. You're welcome anyway .

Thank you again!

 

[Jafrican]

I am having a similar problem with my 4K iMac with 1TB Fusion drive. It was so slow so I started looking for solutions and realised that the Fusion drive might not be working. I saw two drives in Finder and thought I found the Problem. When I tried l diskutil resetFusion in recovery mode it tells me I don’t have a SSD although Disk Utility shows one. Also, I have a strange result when I type diskutil list. It shows 23 (!) disks.
What am I doing wrong?

 

[casperes1996]

I am having a similar problem with my 4K iMac with 1TB Fusion drive. It was so slow so I started looking for solutions and realised that the Fusion drive might not be working. I saw two drives in Finder and thought I found the Problem. When I tried l diskutil resetFusion in recovery mode it tells me I don’t have a SSD although Disk Utility shows one. Also, I have a strange result when I type diskutil list. It shows 23 (!) disks.
What am I doing wrong?
View attachment 874052

That's not weird as such. Disks include virtual disks, and when you're booted in recovery mode, there's a lot of those. I never counted how many I usually get cause I only look at the important ones.
In your case that'd be disk0, your HDD, disk1, your SSD, disk3 and disk4.
Now; Normally a Fusion drive on APFS will have a single APFS container shared between both physical drives. In your case they have one each. Tear them both down (you'll lose all data as I suspect you know trying to reset a fusion), and make a new container that they share. diskutil ap will show a list of commands. If you want more specific step-by-step I can look into the necessary commands for you, but you should be able to deduce it from the command listing and help pages diskutil ap offers, if you have some familiarity with CLI programs (CLI=command line interface)

 

[nambuccaheadsau]

Using Mojave and an APFS formatted drive requires a different procedure. Have a read of this as this is different for an HFS+ drive. Back up first as splitting erases the drives:-

How do I split Fusion drive on Mojave / APFS?

I have a 2013 iMac (27" 3.5GHz i7, model id iMac14,2, EMC 2639) that has a Fusion drive. I want to replace the Fusion's internal HDD with an SSD. My understanding is that I should split the Fusion ...

apple.stackexchange.com

 

[Weaselboy]

It shows 23 (!) disks.

Don't worry about that.... it is normal and those are little virtual drives the recovery utility uses. Try formatting each drive first (backup first) the run the diskutil resetFusion command.

Are you on Mojave?

 

[erajkowski]

help! attempted to downgrade from Catalina to Mojave using a USB boot disk and now my fusion drive is split and cannot see main HD with all my data except in Disk Utility, here is diskutil list above. I need to force remount in an attempt to save data is this possible? I know if i refuse then data will be lost.

Suggestions? Thanks!

(I am currently running yosemite off an SD card but HD are not visible)

 

[casperes1996]

View attachment 891098
help! attempted to downgrade from Catalina to Mojave using a USB boot disk and now my fusion drive is split and cannot see main HD with all my data except in Disk Utility, here is diskutil list above. I need to force remount in an attempt to save data is this possible? I know if i refuse then data will be lost.

Suggestions? Thanks!

(I am currently running yosemite off an SD card but HD are not visible)

You may need Catalina to interact with a drive that has been on Cataline. I don't have experience with doing it on older systems, so I'm only working off assumptions here, but Catalina automatically uses two container spaces for macOS instead of just one, and it wouldn't surprise me much if the specifics of APFS on Catalina are slightly different to prior to it.

You should never attempt a downgrade without having all your data backed up by the way. I would never even try downgrading an OS expecting to keep any data in the first place.

 

[erajkowski]

You may need Catalina to interact with a drive that has been on Cataline. I don't have experience with doing it on older systems, so I'm only working off assumptions here, but Catalina automatically uses two container spaces for macOS instead of just one, and it wouldn't surprise me much if the specifics of APFS on Catalina are slightly different to prior to it.

You should never attempt a downgrade without having all your data backed up by the way. I would never even try downgrading an OS expecting to keep any data in the first place.

Thanks for the quick response! I was able to view the HD after the initial downgrade by installing mojave on a small 10Gb partition but then after a reboot it tried to reinstall new os to the fusion drive which failed (not enough HD space) and now no HD visible or accessible, I guess ill try creating an external bootable drive with Catalina and see if its accessible first. Then just refuse with fresh install if not successful.

 

[erajkowski]

@casperes1996

Hey thanks again for the hint that the specifics of APFS on Catalina may not be able to read by an older OS, El Capitan was unable to view the HD at all but when I ran a Mojave bootable external I was able to view all my data.

Thanks so much again!

 

[casperes1996]

@casperes1996

Hey thanks again for the hint that the specifics of APFS on Catalina may not be able to read by an older OS, El Capitan was unable to view the HD at all but when I ran a Mojave bootable external I was able to view all my data.

Thanks so much again!

You're welcome. And as some of the greatest life quotes go:

1) Always clear all before an important calculation.
2) Always back up important stuff before messing with OS stuff
3) Always ask before wiping Windows and installing Linux on a friends' PC.

The three golden As.

 

[EllieH]

You say you've followed Apple's instructions - what went wrong in that process?
Please post the output of diskutil list

Beware that re-fusing will erase all data.

 

[EllieH]

I know this is an old post, but hope I can get information. I have a 27" iMac Retina, Late 2014, iMac15,1 with a fusion drive. The drive was full, plus getting errors in both HDD and SDD, so I had them replaced. The technician started the install from my TimeMachine BackUp. When it finished, many hours later, there were two drives on the desktop and it was very slow. It was running Mojave, as before. I used Apple's "How to fix a split Fusion Drive" and it didn't work. I'm hoping that you can write out instructions for me. I'm enclosing 2 print outs from Terminal. Thank you very much.