Late 2015 iMac 27 Fusion Drive problems


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Hi. I was applying an update to (10.15.5) my Late 2015 iMac 27, from a copy of the update that was downloaded from Apple to a USB drive, when the process failed to proceed. Contacted Apple Support and they indicated that the Fusion drive was "split", so I spent quite a while with a tech on the phone and they walked me through the process using "Startup Manager" and the Terminal app. Reinstalled Mac OS X (10.15.5) and the performance was horrible.

Made an appt. at my local Apple Store, (50 miles away) but was cancelled due to Covid-19 and the store closing. Back to the phone.

Received instructions on how to "resetFusion", erasing the Fusion drive and then reinstalled Mac OS X 10.15.5 again, and the same result horrible performance.

Running Disk Utility from StartupManager and performing all the possible checks and get the "drive is healthy" result.

Not sure the resetFusion drive actually did what it was because when I was working with the support tech, we were entering some pretty involved commands in Terminal (diskutil cs commands I believe).

I retired to western North Carolina where all the Apple support options are unavailable due to the pandemic, but am thinking about taking my computer back to Chicago where I bought my computer and see if a genius can help.

Thoughts?

JP
 
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Cory Cooper

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Hello and welcome,

Fusion Drives can be a bit tricky when they aren't working right, because they are comprised of an SSD and a standard rotational drive. I personally have never split or reset a Fusion Drive, so I will do my best to help if I can.

I assume you performed some of the Terminal commands in this article to reset the Fusion Drive: How to fix a split Fusion Drive

-Do you have a Time Machine or other backup of your data?
-What kind of performance issues are you having?

C
 
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Cory,

Thanks for replying.

I do have a backup, but not sure how much of it I will be able to use. Not going to worry about restoring right now.

I ran the steps that were present in the Apple support article that you had referenced in your response.

Here are the steps that I've performed, as best as I can remember...

  • My iMac became un-bootable after I attempted to update Mac OS X to 10.15.5 from a USB drive (downloaded once in hopes of applying update to all three of my Mac computers)
  • I have a backup (SuperDuper) which I could not get to restore properly.
  • Contacted Apple support and was elevated to a "senior technician" which is when I went through some involved steps with them entering a few commands to "repair" the Fusion drive basically diskutil list and a few diskutil cs ..... updating some UID values during a Terminal session, then restored to the OS that was installed when initially purchased (can't remember what version, sorry). At this point the computer would boot but response times were horrible, taking 10-15 minutes to get to the "login" screen, then another 10-15 minutes to open a Finder window. Tried to get iCloud to work - a joke.... Attempted to restore full machine from SuperDuper backup which ran for 22+ hours will similar results.
  • Contacted Apple support again and exchanged several emails with Apple and it was finally decided that I should take it to an Apple store and have a Genius run all the diagnostics on it. Was able to make a Genius Bar appointment and the day before my appointment, the store closed due to the pandemic.
  • Attempted to continue to resolve it on my own, ran the "resetFusion" process and reinstalled using a newly downloaded installer for 10.15.5 that I put on a USB drive.
  • Computer boots but response times are still horrible. Commands will execute but take minutes to complete.
I would like to get my machine working again, but without knowing the advanced diagnostic protocols, I'm at a loss.

The Apple stores are still closed in North and South Carolina, closest one open is Knoxville, TN. Considering taking the machine back to the store where originally purchased in Naperville, IL when I return there on October, but not a fan of this alternative.

Any assistance would be greatly appreciated, but I feel that my best recourse is to get it in the hands of Apple - just a matter of "when".

Regards,

Jim P.
 
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Cory Cooper

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No worries.

It sounds like you have done pretty much everything you can there, with Apple's help. If they advised you to take it in for a look, then that sounds like probably the best option. There may be a hardware issue that they can identify with further diagnostics. I would guess itt may need a Fusion Drive replacement.

Sorry there isn't much more to suggest. I guess you will have to determine when/where you are willing to take it to.

Stay healthy and safe.

C
 

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