2019 iMac Fusion Drive Failure — Upgrade HDD to SSD or also Remove Failed NVMe?

The external SSD boot detail is the key data point here. If kernel panics are occurring while running entirely from the Samsung T7, the failed NVMe blade is almost certainly still being interrogated at the hardware level during boot regardless of its APFS status. macOS probes all connected storage at startup, and a failing NVMe controller can generate error interrupts that destabilize the system even when the volume isn't mounted or part of any container.

Replacing the HDD with a SATA SSD without removing the NVMe may improve performance but likely won't resolve the panics if that's what's driving them. The more complete fix is physical removal of the blade, which does require the motherboard flip that -g- described.

One way to get clearer confirmation before committing to the more involved teardown: run DriveDX as suggested and look specifically at what error counts are accumulating on the NVMe. If you're seeing uncorrectable errors climbing, that controller isn't going to sit quietly. If the drive shows as completely unresponsive with no SMART data at all, that can also be the cause — the system may be waiting on it to respond during probe and timing out.

The teardown is involved but not beyond a competent repair shop. Given the machine's specs it's worth doing properly rather than leaving a known bad component in place.

On a 2019 iMac (27-inch, 2019), a failing NVMe blade can still cause system instability even if it’s no longer part of the Fusion setup. Since it remains active on the PCIe bus, macOS may continue interacting with it.

Given that you’re seeing kernel panics even when booting from an external Samsung T7 SSD, the failed SSD is likely still interfering at a low level.

Upgrading the HDD to a SATA SSD is a good step, but for long-term stability, it’s generally recommended to also remove the failing NVMe blade if possible.

akfromnyc wrote:

At this point, I’m not inclined to try running anything off the internal drives. I’m currently booting from an external USB SSD (Samsung T7), and performance is generally good. The only intermittent issues I’m seeing—occasional freezes and a kernel panic—appear to stem from low-level interaction with the failed internal NVMe SSD, rather than the external drive itself. I’ve attached two short excerpts from a recent kernel panic log that show the NVMe timeout directly.

FYI, if you have any external Thunderbolt connected NVMe SSDs, they will show up as "nvme" in the Kernel Panics.

Given that, my working assumption is that if the internal SSD could somehow be taken fully out of the equation (or effectively neutralized), the external boot experience would likely be stable enough that I wouldn’t need to pursue an internal HDD → SSD upgrade.

I would perform a simple erase of the internal SSD so you get rid of any macOS boot files so the system firmware doesn't have to spend much time checking the SSD for bootable volumes which will minimize the chances of the internal SSD causing a problem.

I would also configure macOS to prevent mounting the internal SSD automatically during the boot process. You can use the instructions in the following article....you may need to change "hfs" to "apfs" in Step #8 if you erase the internal SSD with the APFS file system. This will further minimize macOS trying to access that internal SSD.

Prevent a volume from mounting at startup - Apple Community

If you still get the "nvme" related Kernel Panics even by doing both of these things and you do not have a Thunderbolt SSD connected which could be the source of the panics, then the only other options are to try resetting the SSD (I will need to write those instructions, just let me know), physically remove the internal SSD, or retire & recycle the computer.

I take your point on the HDD as well—especially the “High Fly Writes” attribute—which does suggest it’s not in great shape either. That reinforces my hesitation to rebuild the Fusion Drive or rely on either internal disk going forward. At this stage, I’m more focused on isolating the source of instability than trying to rehabilitate the internal drives.

I don't recall seeing any HD exceeding the manufacturer's lifetime expectations for High Fly Writes. This HD seems to have allowed for only 100 High Fly Writes.

According to the SMART wikipedia page, here is a description of High Fly Writes:

HDD manufacturers implement a flying height sensor that attempts to provide additional protections for write operations by detecting when a recording head is flying outside its normal operating range. If an unsafe fly height condition is encountered, the write process is stopped, and the information is rewritten or reallocated to a safe region of the hard drive. This attribute indicates the count of these errors detected over the lifetime of the drive.

This feature is implemented in most modern Seagate drives[3] and some of Western Digital's drives, beginning with the WD Enterprise WDE18300 and WDE9180 Ultra2 SCSI hard drives, and will be included on all future WD Enterprise products.[56]

i would do the backup clone and timemachine backups myself

i would confirm what NVMe SSD part they are installing

i would avoid non-Apple SSD and buy the SSD used off eBay (and supply the part)

the part you want is SAMSUNG SSPOLARIS “pulled from 2019” guaranteed 100 % health (around 1000 hours max) — it will have a date printed on it 2019 or 2020 — I’ve been buying them 2TB at $200 ea but they are $300 currently

the Sintech NGFF adapter and retail m.2 will work but I’ve had issues with them — zero issues with the genuine authentic apple part noted

ive done more than a dozen of these NVMe upgrades in the past year on 2019 iMacs …

Hi akfromnyc,

Notwithstanding the good advice provided in this thread, and given you are looking at considerable expenditure in fixing your 2019 iMac, I suggest you consider a possibly more cost effective DIY solution before making a final commitment. The 2019 iMac is very upgradable if approached correctly. My 2019 iMac as of 2022 has an internal 2TB SATA Samsung Evo 870 and a 2TB WD Black SN770. Fusion no longer required. I can testify that after four years this configuration has worked reliably and the NVME is very fast; (Read 3092MB/s Write 2911 MB/s AJA). Similar experience has been achieved by many others.

If you have the inclination and the aptitude, review this blog which contains all you need to know.

https://forums.macrumors.com/threads/a-list-of-successful-imac-27-2012-2019-ssd-upgrades.2162435/

one 2019 5k i5 with matched set OWC RAM (4x32gb)*

one 2019 4k i7 with 64gb matched set OWC RAM (2x32gb)*

*these two were my personal machines - I still have the 27"

one 2019 4k i5 with 16gb (2x8gb) Apple RAM

two 2019 4k i7 with original 32gb Apple RAM (2x16gb)

ALL ORIGINAL FUSION MODELS

I kept them all running/sleeping here to be sure of zero issues -- because I was selling them

over more than a month of that -- I could not guess which machine would wake with the restart MMIO crash -- they all took turns with about the same frequency

+++++

honestly im not curious about it any more

I had five freshly-erased installs of Sequoia (to 15.7) -- with bare bones installs -- mirroring the problem

replacing the WD sn850x SSDs with OEM Apple SSD SOLVED all problems after weeks of more testing -- I sold the four 4k machines and none of them came back

I JUST CAUGHT THIS:

estimate>> We would replace the existing hard drive with a new 2TB SATA SSD, remove the failed NVMe blade

they are not installing a new NVMe SSD -- only removing it (DriveDX reports it is toasted)

that SATA SSD will provide 500MBs read/write speed

not the 2100/2500 MBs write/read speed of Apple NVMe SSD

+++++

$800 is a lot of money to put in a SATA SSD repair job

(but not a bad price for flipping the main board access)

I would definitely ask them if they could install your used Apple blade when they remove the old one

If you like 2019 or 2020 hardware -- I would start looking for original SSD units in that price range (and sell your broken one for parts, should be able to get $350 with the problem disclosed if the outer is in excellent condition, and the screen is not color fading -- you have 14,000 hours on the SSD -- that's a lot of hours on an SSD -- you definitely got some good out of this machine)

Australopithicus01 wrote:

With respect, tbirdvet, I disagree. 2019 iMac is the last easily upgradable iMac. Yes, breaking and cleaning off the adhesive is tedious, but in all other respects not much different to other imacs of previous years. Having a craft background, I find slicing the adhesive tape using a scalpel with the blade guided by the aluminium edge gives clean and easy cut. Manual strip and clean is easier than wheel which chews the rubber/adhesive. Use wheel to encourage opening and be careful with scalpel around the camera in the unlikely event cable is protruding into cavity.

I would not call opening up an iMac....any Intel iMac as easy even for an experienced repair tech.

There are several very fragile and easily damaged cables & connectors involved just to detach & reattach the Display Assembly. These cables are not easy to detach or reattach as there is very little room & it is hard to see what you are doing. And trying to cut the adhesive could lead to damaging the camera or camera cable. Plus it is very easy to break the Display Assembly itself if it is not handled & stored properly since it is large & heavy. I know a repair tech who removed one and placed it on a table....a while later we heard a loud pop.....the Display Assembly cracked under its own weight.

And that is just to remove the Display Assembly. You are suggesting a user to replace the internal NVMe SSD which is located on the back of the Logic Board. This requires removing just about every component from the iMac including the Logic Board. The Logic Board is not easy to remove or reinstall....it is very easy to damage the board.

I definitely would never recommend an average user from even attempting such a repair. Sure if a person has some technical skills in repairing equipment and is willing to risk accidentally damaging their computer, then they may be successful.

However, with today's current extremely high prices for SSDs I don't think makes economical sense....even less sense if a person must hire a tech to perform the replacement.

Before I would even consider such an option...even if it was economical....I would first try resetting the SSD to factory defaults to see if that can get rid of the SSD's errors. I've saved multiple SSDs by doing so...even some Apple OEM NVMe SSDs (I also bricked one with an experiment which may be just as useful if the internal SSD is still interfering with booting from an external SSD).

Swapping the internal SATA HDD with a SATA SSD is a fast (minimum time) routine job for experienced shop — they would be responsible for any damage

i recommend calling around for a few quotes

i would have to see the DriveDX report on the Apple NVMe — I’ve never seen one of those fail — seen a lot of hdd fail

i would first de-fuse the SSD/HDD and Erase the SDD APFS

then run DriveDx for the health information

you could use it for storage if its still healthy

you might be able to ignore it if it’s bad

upgrading the NVMe SSD is probably 2hrs shop labor — the main board has to be removed and flipped over to access the slot — but if you go that route the machine goes to next level performance and rivals the new iMacs on a couple areas

my main work machine is 2019 5k i5, 8gb video, 128gb ram, 2TB apple NVMe, 2TB SATA SSD that i disasembled and did the SSD upgrades (it was original 2TB fusion)

akfromnyc wrote:

<etrecheck report.log>

Here is the etrecheck report as you suggested. Note that i am booting off external non-thunderbold samsung t7 ssd, and have unmounted the HDD. Thanks!

You should uninstall MalwareBytes or at the very least turn off the real-time scanning option in MalwareBytes. There is no need to have an anti-virus/malware app running all the time. These types of apps usually cause more problems than they solve since they interfere with the OS at a very low level. These types of apps are a known cause for performance issues & system crashes.

Why are you using the Samsung software? Unless you are using it to manage some other external Samsung SSD, you should uninstall this software since it won't do anything for this T7 SSD that you are using to boot macOS. I would even question its use to manage any external SSDs.

Also uninstall PulseSecure by following the developer's instructions. I'm not sure, but it appears it may be an Invanti product for a VPN/Firewall. Unless you are using a VPN to connect to an employer's network, most people have no need for a VPN.....and most VPNs advertised to consumers are not as private & secure as you may think. See the following article for some details:

https://gist.github.com/joepie91/5a9909939e6ce7d09e29

You also have an old Kernel Extension "jawbone" & "aliph". According to the following Wikipedia page the company disbanded years ago so this software is more likely to have compatibility issues and security vulnerabilities. It may be a good idea to uninstall it as well by following the developers instructions.

There are a few other items that may be of concern since they seem a bit older from 2020. I'll leave it to others for a further analysis of the EtreCheck report.

It is also odd that so many areas in the report mention being unable to provide details due to needing Full Disk Access. That is very odd. I would not expect booting from an external drive to cause this problem, but whatever is preventing EtreCheck from providing a full report is also likely causing any performance issues as well.

With respect, tbirdvet, I disagree. 2019 iMac is the last easily upgradable iMac. Yes, breaking and cleaning off the adhesive is tedious, but in all other respects not much different to other imacs of previous years. Having a craft background, I find slicing the adhesive tape using a scalpel with the blade guided by the aluminium edge gives clean and easy cut. Manual strip and clean is easier than wheel which chews the rubber/adhesive. Use wheel to encourage opening and be careful with scalpel around the camera in the unlikely event cable is protruding into cavity.

While SSD’s are no longer cheap, the SN770 is a great performer in this iMac. Add a adapter frame for a SATA SSD as well if you wish. However, just replacing the NVMe is the most economical option as SATA SSD costs money and is only 17% of NVME speed. 2TB - 4TB WD Black are favoured and reliable.

https://www.tonymacx86.com/threads/choosing-a-compatible-nvme-ssd-for-your-macos-boot-drive.323479/

I have the same iMac. I would not recommend opening up that Mac. That model is very difficult to do any internal hardware changes. I would suggest you look at a new Mac (perhaps a Mini M4 with a new monitor). If you can get it to run off an external TB drive that would be the best scenario to save the unit. I would run the free app Etrecheck and post here for analysis. It might provide some info to help diagnose and issues.

im not familiar with "High Fly Writes" or how serious it is on the HDD in this reference (if it is flagged on the screenshot)

DriveDX is reporting the HDD as healthy enough to freshly Erase (as a stand alone drive) and install fresh macOS for testing

if the bad hardware associated with the (freshly erased, APFS) SSD allows the HDD to play nice -- that may provide a clue if you can get by with SATA SSD replacement only (and ignore the failed Apple SSD in place)

AJA System Test will time the HDD -- it should be read/write around 180 MBs if functioning proper