Once and for all: Does MacOS Mojave work with Fusion Drives?

Coconutcreampie

Suspended
Aug 31, 2016
143
73
NY America
I had the same issue eventually. It's a cop out. They want their magic boxes to remain sealed, which is their prerogative I suppose. My prerogative was to move on.
Why did you move on? You just simply need to freshly reinstall Mac OS on the new SSD in that example they used, or wipe the original SSD and install it there.
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I have had a two-month nightmare with Mojave and my late-2014 iMac 27”.
Mojave wouldn’t install on my OEM fusion drive - found problems - so I installed a SATA SSD from OWC. Still problems. Took to apple store. They identified a bad RAM module and installed Mojave for me. Replaced the RAM.

The machine was never reliable thereafter. Ran OK for short intervals before going into molasses mode for most of the time. Disk utility wouldn’t even make it through the volume. Tried to reinstall Mojave and made it worse (woudln’t Complete the process). Eventually it woudn’t boot any more, after hours logged w/apple support.

Was back at apple store yesterday, and the techs there made this jaw-dropping suggestion:
This iMac is designed to work with a fusion drive. So you MUST replace the original HD with an actual HD, not an SSD, and fuse the drives. This seems nuts to me, as you should be able to run from any legit volume — USB external, whatever. Anyone heard this restriction before? Any logic there? Thank you....
I know it’s an old post, but answering in case the information can help others.

1- The original configuration of your iMac was with a Fusion Drive, which is what they were probably referring to. Number two, below, could have also been on their minds.

2- When you installed the SSD (I'm assuming you mean internally?) did you also reformat the SSD part of the Fusion Drive? That SSD resides on the flip side of the motherboard. If you did not then you'd have a conflict with the Fusion Drive SSD no longer seeing the other half of the Fusion Drive, the HDD you removed.

I would wipe both drives and start from scratch. Of course back up your data before hand. If your Fusion Drive SSD is one of the larger ones, 128GB, then I would install Mac OS there, as it will be faster than the SATA SSD that you installed.
 

brofkand

macrumors 6502
Jun 11, 2006
466
909
Why did you move on? You just simply need to freshly reinstall Mac OS on the new SSD in that example they used, or wipe the original SSD and install it there.
I was unable to use the Fusion Drive arrangement of my iMac. I took the 1TB platter out of my iMac 2015 and put in a 500GB Crucial SSD, I was able to marry the SATA SSD and PCIe SSD properly, but was unable to get Boot Camp to work. It's a bug in APFS (I am assuming APFS is the issue because it worked in High Sierra) but instead of fixing it, Apple is saying it's not supported to replace the hard drive in your iMac.
 

Coconutcreampie

Suspended
Aug 31, 2016
143
73
NY America
I was unable to use the Fusion Drive arrangement of my iMac. I took the 1TB platter out of my iMac 2015 and put in a 500GB Crucial SSD, I was able to marry the SATA SSD and PCIe SSD properly, but was unable to get Boot Camp to work. It's a bug in APFS (I am assuming APFS is the issue because it worked in High Sierra) but instead of fixing it, Apple is saying it's not supported to replace the hard drive in your iMac.
You tried to create a Fusion Drive out of two SSDs?! Why? It's not designed for that, nor does it make sense.
 

brofkand

macrumors 6502
Jun 11, 2006
466
909
You tried to create a Fusion Drive out of two SSDs?! Why? It's not designed for that, nor does it make sense.
I had a 32GB SSD in the iMac from the factory, it's useless in any other capacity except to use as a Fusion Drive.

The point is it worked just fine in High Sierra (or perhaps it was Sierra). The functionality broke in the succeeding OS release.

Rather than fix the bug, Apple blamed the users. But that's nothing new for the company. "Simply avoid holding it in that way" etc.
 

Coconutcreampie

Suspended
Aug 31, 2016
143
73
NY America
I had a 32GB SSD in the iMac from the factory, it's useless in any other capacity except to use as a Fusion Drive.

The point is it worked just fine in High Sierra (or perhaps it was Sierra). The functionality broke in the succeeding OS release.

Rather than fix the bug, Apple blamed the users. But that's nothing new for the company. "Simply avoid holding it in that way" etc.
I'm not surprised it broke. I'm betting it didn’t work properly to begin with and you just didn’t know it. The Fusion Drive concept was not made to work with two SSDs. That small 32GB drive could have been used on its own. An iTunes music library would be perfect for a drive of that size. Of course it could be used for any storage you want.
 

naerct

macrumors member
Mar 19, 2019
81
12
Southern NH
Why did I get an email from MacRumors alerting me to a post that was made Oct. 20, 2018?
It looks like they solved the problem for at least stock Fusion drives. Regardless, I highly recommend never using a Fusion drive. I would also not recommend a spindle drive inside. While I find APFS a much better file system for my purposes, There's documented evidence that spinners are not as fast with APFS. Also SoftRAID has little current ability with APFS. So I keep most of my storage on an internal 20TB Raid5 and a 24TB multi bay external enclosure. (a five disk Raid5 gives me read speeds of 450MB/s, triple normal spinner speeds) All my bootable drives or clones are APFS. I used to be able to use RAIDs with Mojave, but not anymore. In one situation I use a WD USB3 8TB as a 3rd backup and a residence for backup clones. The APFS system is much more convenient to delete an APFS volume or create a new one with two clicks. I never assign a size to the volume, and so all those storage drive volumes share all the empty space to all the other volumes in that APFS container. If I actually have to boot from the slow external clone, it can use all the empty space on the drive (for system files and a OS scratch disk) not just what's on the volume. The really bad part of that is that my cMP can only boot from an original USB2 port, not my USB3.1 gen2 ports. However, those drives are so slow, it doesn't make much difference. For fast external boots, I have to use eSATA3 to boot externally. That doesn't work too well for an iMac...
 

davidlv

macrumors 65816
Apr 5, 2009
1,256
21
Kyoto, Japan
My 2014 Mac mini fusion drive got converted automatically to APFS when I upgraded to Mojave. I didn’t notice anything. Had to check the device’s status to discover the conversion.
Check out my post here https://forums.macrumors.com/threads/corrupt-imac-fusion-drive.2220308/
for info on Mojave running on a Fusion drive, splitting that Fusion drive into one HFS+ SSD and one HFS+ HD and now with clones running on both and external USB APFS SSD and the internal HFS+ SSD. It just works (Apple system updates only appear on the External APFS disk, so CCC gets a workout once in while, enough to keep it in good shape.:cool: