Replacing Fusion Drive Guidance?

petercw2

macrumors regular
Original poster
Mar 1, 2003
125
15
late 2012, 27" 3.4 - 1TB Fusion drive is DOA. Replacing w/ a 1TB SSD, but wondering if I need to go thru the hassle of pulling both the spinner and the blade? (i do not know which is failing, but I'd guess the spinner). After watching the videos, it's pretty obvious not having to pull the mother & power boards out would be the preferred move - but I didn't know if because it's natively a fusion, I would need to pull/replace both the blade and spinner - or a single SSD would be the correct solve.

any help or guidance is appreciated (searched the forum and couldn't easily find this answer, just in case you're wondering.)
 

Fishrrman

macrumors P6
Feb 20, 2009
17,474
5,676
My suggestions:

First, can you boot to internet recovery (NOT "the recovery partition")?
(command-option-R at boot)

If you can get there, you could use the terminal to "de-fuse" the fusion drive.

If you can "break apart" the two drives into "standalone" drives, you can then erase and test them individually.

This should give you an idea as to which has a problem.

If the HDD is bad, but the SSD tests out ok, it might be possible to install a copy of the OS onto it and get it running again. I believe the SSD portion of the fusion drive in the 2012 models is 128gb -- not large, but "large enough" to be usable as a boot drive with apps and a slimmed-down user account.

IF you find that both drives check out "ok" when DE-fused, I'd just leave them as separate SSD and HDD, and use the iMac that way. Would save you some trouble!
 

petercw2

macrumors regular
Original poster
Mar 1, 2003
125
15
If you can get there, you could use the terminal to "de-fuse" the fusion drive.
do you know the command to do this in terminal?

I've actually already placed the order for a SSD replacement, but what I really want to know is if I NEED to also pull the blade drive portion of the Fusion when I pull the spinner and pop in the new SSD.
 

eric89074

macrumors regular
Sep 19, 2012
143
147
https://www.lifewire.com/split-fusion-drive-apart-2260166

I'd be willing to bet the spinning drive has gone bad and the SSD portion is still good. If so I'd fuse it with the SSD going in the spinning HD spot. Don't forget you'll need the inline thermal sensor for the new SSD or the fan will spin at full speed. You can get it off amazon. Or you can get a fan adjustment app to turn it down.
 

petercw2

macrumors regular
Original poster
Mar 1, 2003
125
15
https://www.lifewire.com/split-fusion-drive-apart-2260166

I'd be willing to bet the spinning drive has gone bad and the SSD portion is still good. If so I'd fuse it with the SSD going in the spinning HD spot. Don't forget you'll need the inline thermal sensor for the new SSD or the fan will spin at full speed. You can get it off amazon. Or you can get a fan adjustment app to turn it down.

Since it will be the same space size, what if I just wanted to use the new 1TB SSD i'm installing myself? Again, all I'm trying to suss out is if there is a requirement to physically disconnect/remove the blade SSD portion of the Fusion drive for whatever technical reason. its only 128G so not using it AND not having to do the terminal work to recreate the fusion drive and pulling out the two critical boards to access it, probably make it worth not doing. Hope that makes sense.

thanks for everyone's feedback.
 

CoastalOR

macrumors 68020
Jan 19, 2015
2,494
908
Oregon, USA
Since it will be the same space size, what if I just wanted to use the new 1TB SSD i'm installing myself? Again, all I'm trying to suss out is if there is a requirement to physically disconnect/remove the blade SSD portion of the Fusion drive for whatever technical reason. its only 128G so not using it AND not having to do the terminal work to recreate the fusion drive and pulling out the two critical boards to access it, probably make it worth not doing. Hope that makes sense.
thanks for everyone's feedback.
You can remove the blade SSD if you want, but there is no technical reason that requires it's removal. If you leave it in then you would have 2 drives of 128 GB SSD and 1 TB SSD that would appear as 2 drives unless you decided to "fuse" it with the 1 TB SSD.

The current internal 1 TB HDD is 3.5" and the new 1 TB SSD is 2.5" and is therefore too small to fit the existing 3.5" drive bracket.
See Steps 35 & 36:
https://www.ifixit.com/Guide/iMac+Intel+27-Inch+EMC+2546+Hard+Drive+Replacement/15796

Which macOS are you currently using?
 
Last edited:

petercw2

macrumors regular
Original poster
Mar 1, 2003
125
15
You can remove the blade SSD if you want, but there is no technical reason that requires it's removal. If you leave it in then you would have 2 drives of 128 GB SSD and 1 TB SSD that would appear as 2 drives unless you decided to "fuse" it with the 1 TB SSD.

Do you have an internal drive enclosure for your new 1 TB SSD? The current internal 1 TB HDD is 3.5" and the new 1 TB SSD is 2.5" and is therefore too small to fit the existing 3.5" drive bracket.
See Step 36:
https://www.ifixit.com/Guide/iMac+Intel+27-Inch+EMC+2546+Hard+Drive+Replacement/15796

Which macOS are you currently using?

I've purchased a kit that includes all the stuff I need to do this, since it is a "thin" model the screen removal/replacement required some stuff I couldn't get otherwise or at the same price. This includes the SSD enclosure, adaptor.

OSX version: I was on 10.14 and thought it was the source of all my issues, pinwheels and bogging - this whole drama started when I was attempting to downgrade to 10.13 - now that I know it is a dead drive, I hadn't put too much thought into what version I will reinstall.
 

CoastalOR

macrumors 68020
Jan 19, 2015
2,494
908
Oregon, USA
I've purchased a kit that includes all the stuff I need to do this, since it is a "thin" model the screen removal/replacement required some stuff I couldn't get otherwise or at the same price. This includes the SSD enclosure, adaptor.

OSX version: I was on 10.14 and thought it was the source of all my issues, pinwheels and bogging - this whole drama started when I was attempting to downgrade to 10.13 - now that I know it is a dead drive, I hadn't put too much thought into what version I will reinstall.
I have not tried to defuse or fuse a system running Mojave, but I suspect there may be issues in past instruction articles since they discuss core storage commands and Mojave uses APFS containers and not core storage.

I would stay away from fusion if it were me.
 

petercw2

macrumors regular
Original poster
Mar 1, 2003
125
15
I would stay away from fusion if it were me.
my plan is to minimize complications: 1) pull the spinner and replace w 1TB SSD, leave the blade in place 2) reinstall but forgo any attempt to reconfigure fusion 3) double the RAM while inside
 
  • Like
Reactions: CoastalOR

petercw2

macrumors regular
Original poster
Mar 1, 2003
125
15
install and upgrade went fine. all is fixed. thanks to everyone for the support and advice.
 
  • Like
Reactions: CoastalOR