iMac Late 2015 Fusion HDD/SSD Failure?

[LordSpunky]

Spec - iMac Retina 5K 27-inch, Late 2015, 3.2 Quad i5.
Running a Fusion Drive - 2TB HDD, 120GB SSD?

I've been running Catalina - 10.15 as it seems more reliable with my "old" iMac.

I woke up to the iMac loosing the OS, nothing but a Windows 10 Recovery window (I had duel booted previously and there was still a Windows Recovery partition.)
My MacOS was gone, went into Recovery mode and tried to reinstall MacOS and cleared all partitions etc, wouldn't install.
Went round some houses, cleared PRAM, the SSD/HDD separated at some point, ran terminal to join them up. Regardless if I try to install Catalina via Recovery or restore from my TimeMachine the iMac will not complete / boot into an OS. All hardware tests etc I've completed show everything is okay?

Today I used a 1TB external HDD and I've installed Catalina and booted into the iMac - so at least I know most of the hardware is working.
My question is which is faulty, or how do I tell if it is the SSD or HDD? I had my old 2009 iMac apart more times than a Ford Escort so I'm not scared to rip this girl apart and change whatever I need to, but I would like to narrow down the fault first.

(PS if Apple made a decent iMac replacement I would be ordering a new one.....but they've made some crappy coloured, small thingy)

Thanks, peace

 

[rpmurray]

(PS if Apple made a decent iMac replacement I would be ordering a new one.....but they've made some crappy coloured, small thingy)

👍

 

[paardenkapper]

Hi there. My daily driver is the exact same iMac but I run it with catalina and replaced the blade ssd and harddrisk with a SATA ssd which is easier to service.

In regard to your problem: I'd first try if you can re-join the fusion drive with:

diskutil resetFusion

in terminal.

Otherwise you could boot Ubuntu from a pendrive and check the smart status of both drives for obvious errors.
In the long run a larger sata ssd would be best I suppose as they're also quite cheap at the moment.

 

[Fishrrman]

Important question:
Do you have a backup of the Mac stuff that was originally on the fusion drive?

I'm thinking the SSD portion of the fusion drive may have had a failure (either software or perhaps even hardware).

REASON WHY:
The bootcamp partition exists entirely on the platter-based HDD. The Mac OS exists on the "whole" of the fusion drive, both SSD and HDD.

If the fusion drive failed, so long as the HDD was ok, the iMac might still be booted through the Windows/bootcamp partition. Which you were able to do.

Setting up an external boot drive was EXCELLENT problem-solving.

Open disk utility.
Go to the "view" menu and choose "show all devices".
What do you see?
Take a screenshot and post it here.

 

[ignatius345]

My question is which is faulty, or how do I tell if it is the SSD or HDD? I had my old 2009 iMac apart more times than a Ford Escort so I'm not scared to rip this girl apart and change whatever I need to, but I would like to narrow down the fault first.

I'd argue it ultimately doesn't matter which has failed. If it's the HDD that failed, you'll want to replace that with an SSD. If it's the SSD that failed... you'll probably also want to replace the HDD with an SSD -- unless you fancy reformatting the HDD and booting off that, which would be a miserable experience.

Of course you also can replace the stock blade SSD but it's apparently more work and harder to source the right SSD and related parts. Excellent thread about it here with all the gory details: https://forums.macrumors.com/threads/a-list-of-successful-imac-27-2012-2019-ssd-upgrades.2162435/

When my own 2014 iMac Fusion Drive started to die, it was the SSD that was wearing out. I didn't bother replacing it because it looked very involved and the SATA swap was much easier and cheaper and fast enough for my purposes. Opening the iMac up was a PITA, but do-able. I got a kit from iFixit that had tools, a bracket for using a 2.5" SSD in place of the 3.5" HDD, and some new adhesive strips. Couple hours work, most of which involved peeling off old adhesive :/.

The way I handled the data was to first boot off the replacement SATA SSD drive in an external enclosure, get it all set up, etc, and run it for a few days. Then when I opened up the iMac I just installed that and when I was done it booted right up with everything in place.

Oh, also in my experience DriveDx is a good tool for evaluating the drives for failure and pre-failure. There's a demo mode that should get you through.