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Model A1419 / EMC 2806 / Late 2014 or Mid 2015. 3.3 or 3.5 GHz Core i5 or 4.0 GHz Core i7 (ID iMac15,1); EMC 2834 late 2015 / 3.3 or 3.5 GHz Core i5 or 4.0 GHz Core i7 (iMac17,1) All with Retina 5K displays

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Upgraded Failed Fusion HDD to an SSD and now it won’t startup

The original HDD portion of the Fusion Drive failed. I followed the iFixit process, along with the tools, for replacing the HDD with an SSD. I re-fused the blade portion of the Fusion Drive with the new SSD using Terminal. I reinstalled macOS using the Internet Recovery mode and restored from a TimeMachine backup. Everything was working fine for a few hours.

I put the iMac to sleep. Went away for a few hours. When I came back it had a black screen with a gray Ø and a URL for something like apple.com/support/startup, IIRC.

I held the power button down for a long time. Nothing. I unplugged the cord for a minute and replugged it in. Nothing. Cycling the power hasn’t worked. What am I missing? Why won’t the iMac power on?

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Sorry you hit one of the issues linking two SSDs into a Fusion Drive Set. The Fusion Drive configuration was strictly intended to fuse a slow HDD with a caching SSD drive. Here the SATA SSD is too fast so there is a risk of data runout.

Best to pull the Blade SSD out or what I prefer is a dual drive config where the Blade SSD is your boot Drive and holds your Apps which need the speed and the SATA SSD holds your static content like music and vids as well as your completed work. But you’ll want a much larger Blade SSD drive, I recommend at a minimum 500GB and most of my clients use a 1 or 2TB as they mostly do video work. In there case the current project sits on the faster PCIe interface SSD.

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@danj Thank you for the reply. I think you may have a point there. What worries me is is it common for the Mac to not startup or respond to the power button with this combo I installed?

Say I get a new blade SSD to replace the old and do the dual drive setup, how do I know it’ll startup and how is the dual drive different from the Fusion drive setup?

How can I test out the Mac - should I pull the blade and try to startup?

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@ndr13507 - As the name implies the drives are fused together! So the system won’t respond correctly using the internal drive setup. To get around that you could use an external bootable drive using the Startup command Option (⌥) as described here Mac startup key combinations.


So do you have a spare drive which you can setup as a bootable drive?


As far as the internals you will need to scratch the SATA SSD back down as it’s still tied to the PCI SSD.


So… Remove the Blade SSD and using the external boot drive, delete the partition map and reformat the SATA drive you don’t need to install the OS as this will be a data drive. Now install the replacement Blade SSD and using the external bootable drive boot up and then run the OS installer so the blade SSD is the boot drive. Done!

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@danj Hey, thanx again for the help.

Yes, I just created a bootable USB flash drive with Big Sur today.

Also, I’ve got an OWC 1TB Aura Pro X2 Gen4 NVMe in a cart. It’s more expensive than most, but I just can’t find any others to replace Apple’s blade.

TI did try to startup the system again by disconnecting the SSD (the one I replaced the HDD with) and nothing happened. I even tried it with the bootable drive plugged in. Nothing. I also tried reattaching the HDD. Nothing. So, I should just listen to you and pull the blade, huh?

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@ndr13507 - Until you do we really can’t go forward. Hopefully that’s all it is.

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@danj Hey. I removed the blade SSD and replaced it with a 1TB SSD. I reinstalled Big Sur to it - not from the bootable USB tho; I don't know if that makes any difference. It works well. For the time being, it's pure vanilla.

Now, I need to erase the SATA SSD I tied to the original blade SSD as a Fusion Drive. I used diskutil list to find all the mounted drives. I located the name of the SATA drive: /dev/disk1. I tried erasing it using: diskutil eraseDisk APFS SATA /dev/disk1.

Terminal came back with:

Started erase on disk1

Unmounting disk

The volume on disk1 couldn't be unmounted because it is in use by process 0 (kernel)

Error: -69888: Couldn't unmount disk

Is the SATA drive now locked because it doesn't have the blade SSD connected? Am I SOL on it?

Thanks for your help

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NDR will be eternally grateful.
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