opeter wrote above:
[[ How do you disable fusion mode?
Because I would also like to drop an SSD (128 GB) into my used Mac mini (arriving next week) but I did read, that most if you install an SSD and already have there an HDD, that MacOS X install will want to make a Fusion drive. ]]
You are correct -- if you put the SSD into a Mac that already has an HDD installed, and boot up from the recovery partition and launch Disk Utility, in many cases it will -automatically- try to re-create the fusion drive.
I don't believe DU will try to do this if you boot from the HDD, however. The reason is DU can't "construct" the fusion drive if the Mac is booted from the HDD, because that would require modifying the HDD directory (which can't be done when you're booted up from it).
Here's a way that should prevent the "auto fusion creation" in ALL cases:
1. Get a USB3/SATA docking station (also known as a "caddy")
2. When you get the SSD, put it into the caddy and connect to the Mini
3. Boot from the internal HDD and launch Disk Utility
4. Initialize the SSD, and set up as required (you could clone the contents of the HDD to the SSD using CarbonCopyCloner or SuperDuper)
5. Do a "test boot" from the SSD to see that all is well (reboot and hold down the option key until the startup manager appears)
6. If the boot is good and everything looks the way you want, NOW it's time to open the Mini and install the SSD.
Aside -- if you get the right USB3/SATA dock (one that has "UASP" support), you may find that the SSD can boot and run the Mini "good enough" from the dock. You won't have to install it internally. I get read speeds of about 432mbps and writes around 276mbps from my dock. That's good enough for me!