Questions re modifying a Model 17,1 iMac running Mojave to remove the Fusion Drive

My 2015 (Model 17,1 w/OS X 10.14 Mojave) iMac was purchased new in 2017. It was a great system until its Fusion Drive failed. After two unsuccessful attempts to repair the Fusion Drive, I am now concerned whether or not this iMac is reparable: Apple declined to repair a “vintage” iMac, and the “repair” performed by a specialist Mac repair shop was an expensive failure.

The repairability issue seems to be largely due to Apple's proprietary SSD designs. For some models, one can find 3rd party replacement SSDs, but for other models, compatible repair parts are not available from any source. For example, OWC – the primary 3rd party source for replacement SSDs for Apple products – does not make an SSD compatible with my iMac Model 17,1.

Some have suggested that a simpler solution to repair a Fusion Drive is simply to replace it with a single, non-Fusion SSD connected to the iMac's internal SATA cabling. This strikes me as an ideal solution – assuming there are no awkward tradeoffs. This question(s) is intended to discover what – if any – tradeoffs are required for the non-Fusion repair option. It's highly likely I do not know what these tradeoffs might be, so I'll list the ones I can think of & ask those providing answers to list any others they're aware of.

Potential tradeoffs for a non-Fusion repair option:

  • Performance: I'm not very concerned about reductions in classic storage drive performance. SATA3 is never going to equal PCI data rates, but the performance limitations I want to overcome are those that require 60 seconds for a login, and 30 second delays in launching an app!

  • Question 1: Will the non-Fusion repair option eliminate the horribly sluggish performance I see now?

  • Question 2: My Time Machine backup was done on the system when it had a Fusion Drive. Will this backup restore to the non-Fusion system?

  • Question 3: Should the SSD portion of the Fusion Drive be removed from the system, should it remain – or does it make any difference?

  • Question 4: Do you know of any other likely tradeoffs or artifacts wrt a non-Fusion system?

Author: Subham

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