Re: Summary of findings – 2017 iMac (iMac18 ,3) with Fusion Drive issues

On 31/01/2026 16:46, David B. wrote:
> On 31/01/2026 05:24, Paul wrote:
>> On Thu, 1/29/2026 6:15 AM, David B. wrote:
>>> Summary of findings – 2017 iMac (iMac18,3) with Fusion Drive issues
>>>
>>> I’m running a 2017 iMac (iMac18,3) which originally shipped with a 
>>> 2TB Fusion Drive.
>>>
>>> Based on behaviour over time, my assessment is that the SSD portion 
>>> of the Fusion Drive has failed, while the 2TB spinning HDD remains 
>>> functional.
>>>
>>> Current setup and observations:
>>>
>>> macOS Ventura is running from an external 1TB SSD and is stable and 
>>> performs well
>>>
>>> Linux Mint 22.3 is installed on the internal 2TB HDD (spinner) and 
>>> also runs reliably
>>>
>>> The same hardware shows instability only when macOS interacts with 
>>> the Fusion Drive configuration
>>>
>>> Kernel panics previously observed (including namespace 2 / SIGBUS- 
>>> style errors) ceased once macOS was moved entirely off the internal 
>>> Fusion Drive
>>>
>>> This strongly suggests a partial Fusion Drive failure, which macOS/ 
>>> APFS handles poorly when one physical store (the SSD tier) becomes 
>>> unavailable or unreliable. Linux, treating the HDD as a simple block 
>>> device, is unaffected.
>>>
>>> Diagnostic/benchmark tools show reasonable performance for the active 
>>> boot device, but they do not expose intermittent Fusion metadata or 
>>> tiering failures.
>>>
>>> Conclusion:
>>>
>>> CPU, RAM, GPU, and logic board appear sound
>>>
>>> Internal HDD is serviceable
>>>
>>> Fusion SSD blade (or its metadata) is the likely root cause
>>>
>>> Running macOS from an external SSD and Linux from the internal HDD is 
>>> a stable and practical workaround
>>>
>>> Posting this in case it helps others with similar 2017 iMac/Fusion 
>>> Drive symptoms.
>>>
>>
>> You'll need the kit of materials to adhesive the front glass back on,
>> after you cut it away to get inside the unit.
>>
>>     https://www.youtube.com/watch?v=jNlJRTRC_GI
>>
>> They depop the connector, on the motherboards
>> that don't have Fusion as a feature. That video still wasn't
>> good, in terms of showing where all the storage connectors are.
>>
>> Wiki has a description, but you really need to read some of the 
>> references
>> to see how it works. It's tiering and doesn't have sufficient notions of
>> RAID to be called RAID. You can artificially promote files, so they
>> end up on the SSD. It also does not look necessarily, like an Intel
>> technology (like SRT). It's not just some rebranding.
>>
>>     https://en.wikipedia.org/wiki/Fusion_Drive
>>
>>        https://arstechnica.com/gadgets/2012/11/achieving-fusion-with- 
>> a-service-training-doc-ars-tears-open-apples-fusion-drive/
>>
>> It's a shame this will achieve a "Swiss Cheese" on a failure. I just
>> think features like this, and just about all the Intel attempts to
>> do similar, are garbage. Why ? Because the amount of support questions,
>> hair loss on failure, who gives a fuck if something is fast, if it
>> isn't reliable ? Reliability comes first, fast comes second. There's no
>> way we want customers asking AI for advice on "how to step out of
>> a pot of boiling water". Just don't go into the boiling pot in
>> the first place, that's my advice.
>>
>> One repair tech on Reddit, said he'd done lots of Fusion repairs,
>> but he'd never had to open the one that just comes with some
>> SSD and nothing else. So he doesn't know what the connector looks
>> like, from not having to do maintenance on the actual good machine
>> to own.
>>
>> Doing tiered, preferentially writing everything to the faster
>> drive all the time, doing promotions and demotions, that puts a lot of 
>> wear
>> on the fast drive. And really, if you were going to do that,
>> the fast tier should have been Optane. As it could handle
>> a lot more write cycles than NAND. It runs a bit warm, so it
>> would have to be laid out to share a bit of cooling air.
> 
> Thank you so very much for your comments, Paul.
> 
> I'm not sure if I've asked you before. Have you ever explored here?
> 
> https://x704.net/bbs/
> 
> Maybe it's another place where you could share your invaluable knowledge.

Has anyone else discovered the joys of x704?

-- 
Kind regards,
David