How do I install a Fusion Drive

[thewall]

I have a late 2014 27” iMac and I need to install a new ssd, the original HD gave up but I managed to install Mojave but it doesn’t have Fusion Drive, when I put in a new ssd drive how do I switch on the Fusion Drive, am I right in thinking that it is a separate ssd, if that’s faulty how do I find out

 

[benwiggy]

A Fusion Drive is a software effect to make two separate devices behave like one drive. Those iMacs came with one tiny SSD, to provide a faster speed, and a mechanical hard drive for larger storage. If you're replacing the hard drive with an SSD, then don't make a Fusion drive. Just use the SSD as a single drive.

There's no benefit to making a Fusion Drive from two SSDs -- given that the original SSD is tiny: 120 Gb at best.

Remember that if one part of a Fusion drive fails, the whole thing is bricked, with no recovery: you'll have to erase and restore from your backup.