Split Fusion Drive after Apple Repair

[way77]

In May my hard drive died on my 2019 27" iMac, I was running Mojave at the time. After trying to create a bootable SSD to no avail, I finally took it in to Apple store and they replaced the 2 TB hard drive. After getting it back it came loaded w Big Sur. It was incredibly slow. I assumed this was Big Sur related and spent much time trying to streamline things. An Apple senior advisor thought it was a split fusion drive. In disk repair you can see the 128GB portion but the second one under that is grayed out & says not mounted. In About this Mac under storage it only shows Macintosh HD. I think that used to say Fusion drive but if it was split shouldn't there be 2 drives shown?

On a side note, tried setting up an SSD w CCCloner but it will not show up under Startup Options and I've checked external disc security settings via Recovery mode.

This has gone from being my best Mac ever to "tool of the oppressor" mode. Very frustrating.

I've gotten the instructions for repairing this from Apple: create bootable thumb drive, run rejoin fusion drive under terminal and then reload everything which is an ordeal. Anything I'm missing or any advice greatly appreciated.

 

[way77]

Additional screenshot

 

[Realityck]

You need to back up the working volume to a external HDD or SSD using CCC first.

Use Terminal to create a Fusion Drive again with Big Safari

1. Turn on your Mac, then immediately press and hold Command-R to start up from macOS Recovery mode.
2. When you see the macOS Utilities window, choose Utilities > Terminal from the menu bar.
3. Type diskutil resetFusion in the Terminal window, then press Return. (case sensitive)
4. Type Yes for it to run.
5. Now you need to reinstall the latest MacOS again using that from Recovery mode menu.
6. After OS is reinstalled, update it to the same version you were previously using, then use Migration Assistant to recover all your data/files/settings from the HDD backup volume.

Note: If you use Option-Command-R during startup, in most cases you're offered the latest macOS that is compatible with your Mac.

If you want to make a bootable CCC backup look at this post.

​

 

[way77]

Thanks R for the reply. I have the main 2TB fusion drive, an external 2 TB time machine backup and the external 1 TB Samsung SSD that I transferred with CCC but couldn't make bootable. I'd love to try again using your method and see if I can make that bootable.
I'm also downloading Big Sur and making a bootable thumb drive. Is previous advice OK w this setup and when I get to 5 above can I use the thumb drive? Lost 2 weeks of data, designs and tax return when the original hard drive failed so trying to make sure I have multiple backups this time. Thanks

 

[Realityck]

I usually just do a fresh system reinstall over the network in recovery mode instead of booted volume with a full installer, that way with option it even installs the most recent beta if you were previous running that. But whatever works for you is a viable alternative. Still couldn't believe the Apple Genius was such a dork he didn't reset fusion after the HDD was replaced.

 

[way77]

Our internet is slow, slow as in 1 step up from dial up and 2 steps up from smoke signals so when things go sideways at least I have the thumb drive ready. I'll try your post for making the external SSD bootable first. I had previously read on CCC website problems doing that in Big Sur that I also experienced and could never make work. If it works this time than at least I have a working volume and can approach fixing the fusion drive with less fretting. I'm still in a little PTSD from first hard drive failure (it was a Seagate by the way, which has to be the most failure prone option Apple could have selected).

 

[way77]

Instead of using CCC, could I just install Big Sur on SSD and use migration assistant to transfer user data from time machine. Would this be a better approach than using CCC listed in your post?

 

[Realityck]

Our internet is slow, slow as in 1 step up from dial up and 2 steps up from smoke signals so when things go sideways at least I have the thumb drive ready. I'll try your post for making the external SSD bootable first. I had previously read on CCC website problems doing that in Big Sur that I also experienced and could never make work. If it works this time than at least I have a working volume and can approach fixing the fusion drive with less fretting. I'm still in a little PTSD from first hard drive failure (it was a Seagate by the way, which has to be the most failure prone option Apple could have selected).

If you read that thread post I linked you can see the user I was responding succeeded making a bootable. Its works well with Intel Macs with Big Sur.

 

[Realityck]

Instead of using CCC, could I just install Big Sur on SSD and use migration assistant to transfer user data from time machine. Would this be a better approach than using CCC listed in your post?

Sure you can do that. I only suggesting using CCC for making a snapshot in the above procedure before wiping the HDD with resetFusion.

 

[way77]

Thanks R, will give it a shot and let the electrons fly!

 

[way77]

You need to back up the working volume to a external HDD or SSD using CCC first.

Use Terminal to create a Fusion Drive again with Big Safari

1. Turn on your Mac, then immediately press and hold Command-R to start up from macOS Recovery mode.
2. When you see the macOS Utilities window, choose Utilities > Terminal from the menu bar.
3. Type diskutil resetFusion in the Terminal window, then press Return. (case sensitive)
4. Type Yes for it to run.
5. Now you need to reinstall the latest MacOS again using that from Recovery mode menu.
6. After OS is reinstalled, update it to the same version you were previously using, then use Migration Assistant to recover all your data/files/settings from the HDD backup volume.

Note: If you use Option-Command-R during startup, in most cases you're offered the latest macOS that is compatible with your Mac.

If you want to make a bootable CCC backup look at this post.

​

R, since I have the external SSD clone working. After I start up in Recovery mode, fix the fusion drive, can I restart back into SSD, reformat the fixed HD in APFS/guid and then clone from SSD back to newly fixed (hopefully) HD?

 

[Fishrrman]

"R, since I have the external SSD clone working. After I start up in Recovery mode, fix the fusion drive, can I restart back into SSD, reformat the fixed HD in APFS/guid and then clone from SSD back to newly fixed (hopefully) HD?"

Is it really necessary to boot to recovery to use either disk utility or terminal to "re-fuse" the internal drives? (I ask because I've never been in a position to actually try it myself)

I'm thinking you might be able to do this while booted and running from your external boot drive.

BE SURE that anything you want to have backed up, IS backed up first !!!
RE-fusing the internal drives will DESTROY any data that is currently on those drives!

Another thought:
If it was me, I'd leave the internal drives UN-fused.
The SSD portion (which is 128gb) will run faster as a "standalone SSD" than it would as part of a fusion drive.

I'd set up the 128gb SSD as "the internal boot drive" (with OS, applications, and slimmed-down home folders).

I'd set up the platter-based internal HDD as "a data drive".

And run it that way.
But... that's just me.

 

[way77]

"R, since I have the external SSD clone working. After I start up in Recovery mode, fix the fusion drive, can I restart back into SSD, reformat the fixed HD in APFS/guid and then clone from SSD back to newly fixed (hopefully) HD?"

Is it really necessary to boot to recovery to use either disk utility or terminal to "re-fuse" the internal drives? (I ask because I've never been in a position to actually try it myself)

I'm thinking you might be able to do this while booted and running from your external boot drive.

BE SURE that anything you want to have backed up, IS backed up first !!!
RE-fusing the internal drives will DESTROY any data that is currently on those drives!

Another thought:
If it was me, I'd leave the internal drives UN-fused.
The SSD portion (which is 128gb) will run faster as a "standalone SSD" than it would as part of a fusion drive.

I'd set up the 128gb SSD as "the internal boot drive" (with OS, applications, and slimmed-down home folders).

I'd set up the platter-based internal HDD as "a data drive".

And run it that way.
But... that's just me.

I was thinking that too, but Apple specifies doing this from recovery mode.

Yes, I know, everything goes bye bye. I was able to clone main drive to an external SSD so I'm operating out of that now.

Never considered using it unfused, that's not a bad idea but before the fertilizer hit the oscillator the fusion drive was very snappy so I'm very OK with getting back to that, plus now I have the external SSD which so far seems quite similar to the fusion from a speed standpoint.

 

[Realityck]

Another thought:
If it was me, I'd leave the internal drives UN-fused.
The SSD portion (which is 128gb) will run faster as a "standalone SSD" than it would as part of a fusion drive.

I'd set up the 128gb SSD as "the internal boot drive" (with OS, applications, and slimmed-down home folders).

I'd set up the platter-based internal HDD as "a data drive".

And run it that way.
But... that's just me.

The size of the SSD (128 GB) is kinda small as a boot volume for a lot of people, if you offloaded some applications data to the 2TB HDD you would really notice how slow reading and writing is. Most HDD is 120 MB/s, where the SATA 3 SSD is 520 MB/s. What makes fusion a interesting solution is the interleaving of files so the most used system, application, data as long as it remains cached it runs fairly fast. Not SSD, but still way faster then the HDD. It for that reason this hybrid worked well, although it’s way slower then the latest Mac PCIe SSD interfaces now, and the SSD prices have really fallen.

 

[way77]

Do you see any problem cloning from external SSD back to re - fused HD? Would it need to be reformatted first as well?

 

[Realityck]

Do you see any problem cloning from external SSD back to re - fused HD? Would it need to be reformatted first as well?

Once the resetFusion is done, it’s just installing the OS then use migration assistant to port your settings, apps, and files from the external SSD, and it’s done. You could do also your clone back to the internal fusion.