This mini has a different port layout than the older models.
This series has one SATA port and one PCIe blade port for a custom Apple SSD. So, this gets into the question on what you have now as that will dictate what you can do.
If you have a HD version of the system you will need to get the PCIe ribbon cable to then add in the custom Apple SSD. sadly, Apples options are quite limited here as they see this SSD as part of a Fusion Drive set unless you get the 2.8 GHz model which allows you to get it configured with a 512 GB or 1 TB SSD. a warning here the larger Apple SSD's are hard to find and are costly!
OWC has a tease page on their web site on having some options coming this spring so you may want to wait a bit here OWC Upgrades for:
2014 – Current Mac Mini.
OK, what if you have a Fusion Drive'd or a SSD model. You options here are larger. While the I/O of the SATA port is slower than the PCIe there is more possibilities using it.
Lets start here with a SSD only model then you'll need to get the needed SATA ribbon cable to add in the drive. Here is the IFIXIT kit you'll need: Mac Mini Dual Drive Kit - Complete Kit.Then you have a choice on what HD or if you can swing it large SSD to put in.
If you have a Fusion Drive config you'll need to first break the fusion drive set before you alter things if you don't you can't connect your old drive back in as it will confuse your system.
If you plan on putting in a SSD you don't want to re-enable Fusion as a dual SSD config under Fusion is slower and does not offer any real benefit.
Hopefully this explains things.
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