I’ve upgraded to Mojave on my 2018 MacBookPro with no significant issues. However, I also own a 2015 iMac with a 3TB Fusion Drive with over 2TB of data.
I understand that Mojave will convert the Fusion)?rive to APFS. Has anyone on this list already upgraded in a similar circumstance (or seen reports of others doing it?). I’m interested in any problems encountered and also in getting a rough idea of how long the conversion of the ‘drive’ will take.
Thanks in advance for any information.
No personal experience, but I’ve yet to hear from anybody who did so having an issue.
It’s difficult to judge how long it takes to do the conversion since it takes place as part of the installation process, but when I did it using an SSD it appeared to be a matter of less than a minute.
-Al-
My experience: With a Mac Mini (2014) Fusion drive.
When I updated to Mojave, it automaticly converted my built in drive to APFS.
But the external spinning drives did not.
You can use Disk Utility to convert external drives to APFS.
All this was seamless and fast.
To perhaps close out this thread:
I took the plunge and upgraded the iMac to Mojave this evening (after creating 2 external clone backups) and running Disk Utility to check for drive issues. I deliberately had no external devices (except for keyboard and pointing devices connected. Anyway, the upgrade took less than 2 hours and all appears well with the Fusion Drive converted to APFS.
I’m hearing that Mojave has trouble with Macs where the Fusion drive was replaced with an SSD.
I have a 2012 iMac that shipped with a Fusion drive (3TB). I replaced the SSD with a 1TB SSD which Is my boot drive and I use the 3TB rust drive for large sets of data.
No problems for me with Mojave other than my machine is 6 years old.
Apologies if this is a tangent. But after updating Adobe CC in October, I had a serious (startup partition destroying) crash. I still (even after another one!) haven’t figured out the cause, but I did discover that my SSD was appearing and disappearing, and during this all I split the fusion drive.
My question is this, however: Is the SSD portion of my (late 2014) iMac Fusion drive built into the drive itself, or is it a separately mounted SSD (which I’m not sure would fit), or is it a card on the motherboard? I could not find any specifics on my hardware. The closest I found was a MacFixIt tear down that suggested the latter. But I’m not going to spend $50 and 43 steps to crack open my iMac and find out! 
I’m still encountering mysterious crashes, even after switching to an OWC external SSD and upgrading to Mojave – always (I think) in Photoshop. Would love to get back to one crash a quarter rather than 2-3 per day.
Boy, tough question. The iFixIt teardown or repair instructions are the best resource I can think of, short of finding someone who’s an active Apple repair tech and knows exactly what’s in there. It does seem as though it would be worth replacing entirely, given the wacky nature of the crashes.
The 2017 iMac 27" is a custom M.2-style blade, and, unless something has changed, it is an Apple-only part, available only on eBay and the like for exorbitant sums.
It’s unlikely that the SSD itself would just randomly fail and return, and while not impossible, I’d be more suspect of the mounting socket; either its contacts with the SSD blade, or a defective connection to the board itself; or a faulty power connection to the drive/controller. All you can do is open it up, remove it, inspect and clean the contacts/reseat the blade, and inspect the socket connection on the board, looking for bad traces.
I hope I’m wrong; maybe just an expensive used SSD will be your cure; but, if not, you can again resell the SSD for little, if any, loss; and then consider obtaining an entire logic board (usually, but not always, comes with SSD).
Alternatively, good Mac repair shops who do genuine board level repairs may be able to fix it for under $300.
EDIT: Another alternative is to replace the HORRIBLY SLOW, variable-speed Apple OEM HDD with a really fast, QUIET 7200RPM 128MB cache (such as Iron Wolf Pro) if you need reasonable performance and lots of space, or just replace the HDD with a good 2.5" SSD of adequate size, if speed is your bigger need.
I have zero experience with this company, and I can’t tell for sure if these drives are new, or even have a trustable warranty, but there are indeed now apparently third party upgrade kits for 2014 (and other) models now (be sure you enter your exact model ID).
e.g.,
After looking around at iFixit I also found this. I have no idea if it really works, but the claim is it will allow you to take a regular M.2 blade SSD and hook it up to the iMac’s blade socket.
http://eshop.sintech.cn/mobile/ui/product.php?id=1002&s=3085093648850
And here’s some pics from a guy who apparently used it.
Sweet! I wish this had been available a year ago; I searched high and low for an option.
The OEM SSD is still slightly faster, in theory, due to the custom Apple silicon controller, but I’d love to see benchmarks versus a 970 EVO Pro. The best news is it should allow for use of fat, inexpensive M.2 blades, which have recently plummeted in price. This will be a great way to extend the life of these aging machines, especially for those who put in the smallest available size in order. I wonder if the newer 2TB blades will be recognized.
Thank you all! I really appreciate the great answers and resources. I agree that the coming-and-going of the SSD is weird, but definitely happening. Just wish opening this iMac was as easy as my old Mac Pro! (:::sniff!::: having pegged out at 10.7.5, it barely runs Chrome anymore!)
