is there a limit to the size of drives used when making a fusion drive?

[prvt.donut]

If the 2012 Mac mini can fit 2x 2.5” drives, could I use a $130 500gb SSD and $160 5TB hdd to make a 5.5GB fusion drive for $290?

 

[DeltaMac]

Your "key" is the physical height of that 5TB HDD.
The 2012 mini is limited to 9.5mm thickness for each drive. The SSD will not be a problem. The HDD will depend on specific drive.

For example, this Seagate 5 TB can't be fitted inside your mini.

 

[Juicy Box]

Your "key" is the physical height of that 5TB HDD.
The 2012 mini is limited to 9.5mm thickness for each drive. The SSD will not be a problem. The HDD will depend on specific drive.

For example, this Seagate 5 TB can't be fitted inside your mini.

Good point, if this was me, I'm not sure I would have accounted for the physical size of the drives.

What about in the software side of things, which is what I think the OP was asking about. Is there software limitations for making a Fusion Drive?

 

[DeltaMac]

Good point, if this was me, I'm not sure I would have accounted for the physical size of the drives.

What about in the software side of things, which is what I think the OP was asking about. Is there software limitations for making a Fusion Drive?

I think you would be correct, although "size" can be interpreted in several different ways.
I am fairly certain that the 5 TB SATA drive would be OK in the 2012 mini.
The limit that the Mac system software (macOS later than version 10.5.3) can support is something like 8 Exabytes (8 million TB), so there is essentially no practical limit to the size when the hardware for that size does not yet exist...
That doesn't exactly answer your question, but I think that I can safely say that you can make a fusion drive with the largest devices that you can find, and the macOS should support it.
But then, it would probably be less cost-effective if you would be spending several thousand dollars on one of the high capacity SSDs --- when you would probably be a lot better off using a large SSD by itself --- not tied by software to a spinning hard drive, and then using spinning storage as needed, as another storage drive, and not as part of a fusion drive.
Does that make sense?

 

[Fishrrman]

My opinion only, but...

... there's no point in "fusing" a large HDD with a large SSD.
It will only slow down the SSD (eventually), and introduce the software complexities of "fusion".

Better to run the drives as TWO "standalone" drives and let things go at that.

If a large capacity platter-based HDD won't fit inside, just attach it with USB3.
Probably next-to-no "slowdown" at all by doing so.