Replaced fusion drive with full SSD, type still listed as fusion. Does this matter?

Hey all. Wondering if a fellow MPU can help me out with a quick question.

The hard drive portion of my fusion drive on my late 2015 27" iMac recently died. I took the opportunity to replace it with an SSD, fusing the SSD blade that is currently in there with a new 2.5 inch SSD so that I don’t have two partitions. Everything thing is working great, but noticed that under “About this Mac” and in Disk Utility, the drive type is still listed as “Fusion”.

My question is: does this matter at all? Is there some way I can make the Mac recognize the drive as full SSD and not a fusion drive? My understanding is that fusion drives were not updated to APFS. Will my file system be upgraded to APFS with the new MacOS when I update? Can I force the move to APFS?

Any help would be much appreciated! I can’t seem to find satisfactory answers while Googling.

Also, for those who were wondering, it was a super easy replacement and I am so happy with the upgrade. The fusion drive, while faster than full HD, was still disappointingly slow. Now that I have all SSD, my computer feels brand new. I bought the upgrade package from Other World Computing which came with everything- 2.5 inch SSD, bracket, and temperature sensor. It also came with tools, but I wasn’t about to try to do it myself. I took it to an Apple Certified Service Provider near me and they did it in a day for $50. Absolutely worth it. Between this and the ability to upgrade the RAM as I please, I feel like this computer should still have a ton of years on it.

This could be problematic, if the OS sees a partition-part of a Fusion drive that is not really there. That’s one issue

Right now if the OS sees it’s a Fusion Drive it will not format as APFS, though Craig Federighi said in May it would be addressed ‘very soon.’ So that’s another issue.

You might want to look into what macOS thinks your ‘fusion’ is comprised of. Launch Terminal, and at the prompt enter:

diskutil cs list

Press enter or return.

Terminal will display an overview of your Fusion drive. Actually, it will display all volumes that are seen as comprising the Core Storage system (which for most people will be the internal drive or the SSD+HD components of the Fusion drive). For real Fusion drives the ‘Logical Volume’ drive will consist of two different Physical Volume UUIDs (Universal Unique Identifiers). That’s what you’ll see with normal Fusion drives - I have no idea what you will see, which is why I suggest you take a peek (without making any changes in Terminal).

This is what I see:

±- Logical Volume Group 3F27EF88-E9B0-475D-8843-AD3709595323

Name: myLogicalVolGroup
Status: Online
Size: 1022898851840 B (1.0 TB)
Free Space: 45056 B (45.1 KB)
±< Physical Volume 399C08FE-7811-4215-B66C-23E7B66096FD
| ----------------------------------------------------
| Index: 0
| Disk: disk0s2
| Status: Online
| Size: 999860912128 B (999.9 GB)
±< Physical Volume 88E895CE-892E-4A1F-8E0B-6930B6D0AC83
| ----------------------------------------------------
| Index: 1
| Disk: disk1s2
| Status: Online
| Size: 23037939712 B (23.0 GB)
±> Logical Volume Family DFE11B75-881D-4BC9-9E85-7AB4E70BEE11

Encryption Type: None
±> Logical Volume 4D835CE5-8255-459D-9EDF-C671FF45D5AC

Disk: disk2
Status: Online
Size (Total): 1012232486912 B (1.0 TB)
Revertible: No
LV Name: Macintosh HD
Volume Name: Macintosh HD
Content Hint: Apple_HFS
LVG Type: Fusion, Sparse

You have a fusion drive! It’s just fusing your new 1TB SSD with the original 24GB SSD that you didn’t remove.There is no good reason to have it set up this way as it would just be slightly slower and less reliable (if either drive fails, the whole thing fails).

You can search for instructions online for unfusing the drives, but note that all the drive contents will be deleted so you will probably want to make a clone of the drive contents first that you can restore from.

ahhh. Ok. I was thinking that fusion only refers to a SSD and a HD, but that makes sense. The guy who did it suggested not to fuse them, but I asked him to so I could just deal with one pot of storage. I didn’t realize that there would be a performance hit. Do you suggest unfusing them (is it enough of a hit that I will notice?), or do you think I should just wait for Apple to support APFS on fused drives?

Thanks for the help!

An odd configuration like that seems like it would be ripe for bugs/issues. I’d say unfuse them and just ignore the 24gb drive.


If you just toss the 24GB drive that’s only a 2½% loss of capacity.