Failing HD in 2017 iMac 5K 3TB Fusion Drive

The Family iMac (a 4.2 ghz core-i7, 64 GB RAM, 3 TB Fusion, Radeon Pro 580 8 GB) has a failing Fusion drive - the HD is throwing SMART errors.

TTP 14 says the SSD component is 69% used, so it looks like it’s time to replace the hard disk.

Anyone have any recommendations?

I was thinking of the 4.0TB OWC 6G SSD and HDD Kit for 27" iMac (2012 - 2019), but I’ve never opened an iMac and at $609.99 - unfortunately that’s nowhere near an M1 iMac’s price if you add Apple outrageously priced SSDs.

I suppose I could have Apple simply replace the HD, but in 2018 that ran $271 for an out-of-warranty 2014 5K iMac, and like I said TTP says the SSD component of the fusion drive is 69% used (though it does say there’s 100% available spare).

Anyone have any advise? Pull it apart, toss the 128 GB SSD, replace the 3TB HD with a 4 TB SSD (or can you just replace the 128 GB SSD with the 4 TB and toss the HD)? Just how hard are these puppies to open up and replace components anyhow?

This kinda cheeses me off - the 3 TB HD in my 2014 5K iMac died after around the same amount of time - 4 years. What kinda cheapo drives are they putting in these machines anyway? They were both purchased as (at time time) as top of the line iMac 5Ks, after all.

Anyone know of a Mac repair shot who will do a disk upgrade like this? I’m just down the road from OWC.

– Thanks, Verne

Um, OWC itself offers that service.

Here’s a link.

They might not be the most cost-effective (you have to compare for yourself), but they do all the things and have all the right tools.

I’ve opened up a number of iMacs, and they don’t intimidate me, but I think you’re right to outsource this.

And if you do this, ditch the hybrid setup and have them install a full SSD. The hybrid drive is exactly what it implies: a transitional solution that addressed the need for speed while acknowledging how expensive large-scale solid state storage was 10 years ago. As you discovered, the Achilles’ heel part of the setup is the spinning hard drive. Get rid of it, and you get a much faster Mac.

I agree with @Matt_McCaffrey. I’ve replaced the SSDs in two 27-inch iMacs now and while it’s doable, it’s not quick or particularly easy. Get OWC to do it.

One note. I strongly recommend making sure that they remove the old SSD and replace it with a blade SSD designed for the iMac. Because you have a Fusion Drive, the other approach would be to just remove the hard drive and attach an external SSD to the hard drive’s SATA cables. That will work, and it’s a much easier disassembly, but on Josh’s old iMac, leaving the bad SSD in place caused it to be super flaky. Getting the SSD out requires taking the entire motherboard out, so it’s a lot more work. But it’s just not worth the pain of cutting the screen off if you’re not going to do that.

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I followed the link and I see 'em mention the 2010 and 2011 iMacs … not the 2017 iMac 5K.

I’ve sent them a query but haven’t heard back from them.

I do want to ditch the fusion drive and just get a straight SSD - I would’ve gotten a straight SSD but they didn’t have enough capacity (max 2 TB at the time). Well, that and you need to possess a small country that you could sell to pay for it.

I followed Matt’s link and it mentioned an OWC upgrade service, but they only mentioned 2010 and 2011 iMacs, and mine is a 2017 iMac 5K. I’m hoping they just didn’t update the web page, but it’s tough to imagine that they would’ve just left it for that long.

Didn’t iMacs used to have magnetic screen attachment, and wasn’t that replaced by adhesive tape at some point? Maybe that was back when they were magnetically sealed.

It’s sort of amazing how far top of the line iMac 5Ks have come in just three years - the 2014 and 2017 were pretty similar, but my 2020 is scads better.

Anyway, here’s hoping that OWC will upgrade the 2017 - I’m just not looking forward to doing this job by myself.

Also, what’s a “blade SSD”? I’m not familiar with the term. Is that some kind of proprietary NVMe slot kind of thing?

The SSD portion of the fusion drive is still operable and is only 69% used (according to TTP). It also seems to be saying that it has 100% of its spares, so why they’re indicating it’s 69% used is a mystery - I thought the only thing contributing to an SSD’s death was writes damaging frames causing exhaustion of the spare frames. I’d imaging if nothing were accessing it it would still have a pretty long service life, though the extra drive showing up in the drive queue would be annoying.

IIRC, it’s the TBW (terabytes written) that drives SSDs going bad, and if there’s no access I wouldn’t think that it would degenerate further. Can the built-in SSD be ripped out or does it have to be replaced with another SSD?

Once the HD was replaced, I could just format both drives as independent and not merge them into a fusion drive.

If you can’t afford a huge SSD (e.g. 2TB or more), then consider a smaller one, in addition to a hard drive. Not fused together - just two separate volumes.

You can store the OS and your apps on the SSD and put things like media collections on the hard drive, where performance isn’t as critical.

This can be done internally (using the connectors your iMac is currently using for the fusion drive) or externally (using Thunderbolt connectivity).

Yes, they once did - magnets to hold the glass to the case, and a screen under that that comes out with a few screws. But that was a long time ago. Today, they’re glued shut like iPhones. You need a tool that can cut through the tape (but not cut any wires that are near the edge of the screen) in order to remove the screen. And you need to replace the adhesive when you close it up again afterward.

WRT “blade SSD”, @ace is referring to one on a small circuit board, not in the shape of a hard drive. For example, here’s OWC’s equivalent replacement. According to iFixit, replacing the blade SSD is a time consuming process, requiring a near-complete teardown in order to get access to its socket. More work than I’d be willing to do.

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Hi Verne,

Just to piggyback on what the others said; I just finished taking apart a 27 inch iMac, pulling out the “blade” SSD, and replacing it with an OWC 1TB version. I ended up leaving the spinning HD in place, mainly because I didn’t have anything to replace it with, and I was worried that disconnecting the combination SATA cable and sensor cable and leaving it unconnected would make the fans spin up all the time. (I’ve still not found a satisfying answer to that; oh well).

As the others have also said, doing this task requires two major steps - removing the adhesive around the iMac to take off the screen, and removing nearly all of the components to get to the blade SSD, which is stored on the motherboard. I wouldn’t do this unless you want a fun challenge (I did). If you do, the SSD replacement kit from OWC is excellent. All of the tools that you will need are included. I think that the 1TB version with tools, etc. was around $245. YMMV. There’s a semi-proprietary connector from the SDD to the motherboard that OWC has somehow replicated. Other manufacturers don’t seem to have that connection, and the fit of the SSD onto the motherboard is a little more dicey.

The videos on the OWC site are also excellent, and provide great step by step instructions. I’ve seen other videos on other sites about this procedure, and the OWC version is the best.

The only extra step that I would take if you do it yourself (before you start the screen adhesive procedure) is to connect the iMac’s screen back up and then use blue painter’s tape to tape the display back onto the iMac’s frame temporarily. That way, you can try to boot up the computer to make sure that you’ve connected everything up properly. If you have, either the computer will boot or the drive will at least be recognized, and then you can again disconnect the display cables so that you can proceed with the screen adhesive installation without fear that you did something wrong.

As for that hard drive, I left it inside the iMac. It’s still working, so I use it as a Time Machine backup for the iMac, and it’s working beautifully. The new 1TB SSD in there makes this iMac feel like a brand new machine.

Whether you do this project yourself, or have it professionally done, I think it’s worth the time and the money.


Yeah, I’m not going in a cutting and doing the dust removal thing. It’s a nice (and expensive) display and I don’t want to take a chance on messing it up.

I’ll leave the old 128 GB SSD in place, and am having OWC replace the rotating disk with a 4 TB SATA SSD - maybe I’ll put a recovery system on the 128 (instead of TTP 14’s eDrive thing) and install Big Sur on the 4 TB drive (and maybe a boot camp). If I had something high access and small I’d put it on the 128 GB drive due to it’s superior speed, but I can’t think of anything. I couldn’t do the blade drive alone because that only goes up to 2 TB.

I’ve already made the arrangements and packed it up to shipped it to OWC - I would’ve preferred to cart it to OWC personally, but everyone there is working from home so they won’t take physical delivery except from carriers. That adds another $58 for UPS ground for the job, which is a shame because my entire family has had 2 Pfizers and OWC is just a couple of suburbs away.

I’ll restore using Migration Assistant from the clone or one of the two valid Time Machine drives - the Time Machine on the Synology seems to have corrupted itself and I’ll have to redo it anyhow because of the new size of the boot drive.

Even though it’s still SATA I expect the change should improve access speed - and after this is done I should never have to deal with another spinning disk. That fusion drive has been the bane of my existence for some time - you could never tell moving from one OS to the next if I’d have to reformat and restore it from backup.

Definitely. SATA’s top speed is 6 Gbit/s or 750 MB/s. That is about 3x faster than the fastest hard drives. (See also Ultrastar DC HC510 datasheet, where this drive lists a maximum sustained throughput of about 250 MB/s)

I had OWC replace the rotating 3 TB drive with a 4 TB SATA SSD, and installed Big Sur (11.3.1) on it and it boots fine in macOS. I then used Boot Camp Assistant to place a 497 GB boot camp - doesn’t it drive you crazy that you can’t specify a value for the size of your boot camp? - and installed Windows 10 and Office and updated it to 20H2.

Both macOS and Windows boot fine.

I then installed Parallels Pro 16.5 to run the boot camp Win partition as a VM - and it craps out with an Error Code 0xc000000f.

Still boots fine in macOS and Win - but Parallels repeatedly dies trying to start the machine with a BSoD, whether the disk is formatted and macOS is installed from Mac Internet Recovery Mode or an 11.3.1 booted disk using the standard installer.

I called OWC but they’re mystified, and I sent the problem on to Parallels but haven’t heard back from them.

Interesting factoid: BCA didn’t ask me for the location of a Windows ISO … does this mean that BCA loads the Win 10 image straight from Microsoft now?

(Several of my BCA builds were redone because I was afraid that it was using an old, obsolete Win 10 Image somewhere but I couldn’t get BCA to prompt for an ISO to use).

If I don’t hear back from Parallels soon, I may give VMWare Fusion a try.

I’ve pretty much decided the rotating 3 TB drives Apple put in fusion setups are crap - my 2014 iMac 5K and the 2017 both died or started throwing SMART errors after 3 - 4 years or so of use.

On a more positive note: the 2020 iMac 5K (core-i9 3.6 ghz, 128 GB OWC RAM, AMD Radeon Pro 5700 XT 16 GB, 4 TB SSD) and Xbox controller are running Mass Effect Legendary Edition at 5120x2880 with 4K assets just fine, though it runs pretty choppy under Parallels at 1920x1080 - so though this is scarcely a game machine, my Last great Intel iMac strategy has paid off :blush:.

It’s a shot in the dark here, but I’m guessing that one or more of the Boot Camp device drivers are incompatible with the virtual environment that Parallels provides, causing the problem.

Can you try making a clean Windows install to a Parallels VM? If that works, then a better solution might be to work with three storage volumes:

  • The Boot Camp volume, to contain the Windows system when booted natively
  • A Parallels system volume (which can be a disk image), to contain the Windows system when running in a VM
  • A data volume, which both systems use (as a “D drive”), to store your documents and maybe even home directories. So your content can be shared between the two systems.

You could probably use the Boot Camp volume as Parallels’ data volume as well to simplify this a bit more. Especially since Boot Camp created a half-terabyte volume for the Windows system.

Apple has used Seagate consumer-grade (not Enterprise) drives for a very long time, but they are not the most reliable. They tend to wear out a bit faster than other brands, and a few models have been extremely unreliable.

My experience with hard drives over the past 30 years is that, in general, they are pretty reliable, but some brands/models are definitely better than others.

My most recently assembled drives have been made from Toshiba N300 NAS drives - they’re designed for 24x7 operation in NAS devices. They are working well, but I only bought them in November, so they’d better be working well!

Before I got the Toshibas, I used Seagate NAS drives, which have not been as reliable as I would have liked - one out of the three drives I purchased failed after a few years and needed replacement. Before that, I used Seagate Constellation enterprise drives, which lasted for the entire time I was using them

I do not recommend consumer desktop drives (e.g. Seagate Barracuda or WD Green) any more because they are explicitly rated for only 8 hours a day usage. They are expected to be used in computers that are turned off (or at least put the drives to sleep) when not in use. That’s no good for me where the computer acts as a server for my LAN and at least one drive (the Time Machine volume) is accessed every hour.

Strangely, my oldest drive (a Seagate 296N - 80MB, SCSI, 28ms seek time) still works great. I moved it from its computer to an external enclosure many years ago and aside from needing to be re-low-level formatted at one point, it has kept on working. Of course, I only turn it on once in a while in order to prove it still works. I keep it around in case I should ever manage to get a SCSI card for my Apple IIGS - an 80 MB drive would work great on that computer.

This is the family Mac, and I’m putting boot camp on it since it’s a it would be nice to have feature.

I’m willing to wait for Parallels to get their act together - heck, on the OWC sales page for the drive I bought it even has a special offer for Parallels on it.

My most recently assembled drives have been made from Toshiba N300 NAS drives - they’re designed for 24x7 operation in NAS devices. They are working well, but I only bought them in November, so they’d better be working well!

Yeah, I use Toshibas in my disk arrays too - the problem is there is no good brand of disk drive since every drive is like a bottle of wine: good this year, bad the next.

I used Seagate Ironwolf drives in my arrays before the Toshibas - the 10 TB drives were great, and I switched to Toshiba when I went up to 14 TB drives.

I used to read a lot of discussion boards trying to determine what drives are good and which are not, but they tend to be filled with religious anecdotes - now when I’m going to buy a RAID drive capacity I go to Backblaze’s excellent reporting blog where I can get real reliability numbers on a massive number of drives used in a 24/7 RAID environment.

The problem when dealing with something like a 3 TB drive is that I’m not sure anyone makes them any more, and who’s got a time machine to go back and determine what the reliability of those drives were back when they were still being bought? Reviews tend to be written at the time of drive introduction and don’t track reliability long-term, and discussion boards tend to be filled with user posts with axes to grind. I know that Seagate had a bad patch a while back, and it could very well have been in the 3 TB consumer drive era.