1 
1 Can the SSD be upgraded?
I have a MacMini like yours. Already replaced the factory HD with a Crucial MX 100 SSD and it's a lot better. I now want to place also a PCIe SSD in order to have a fusion drive. Makes no sense? NO! Although both are SSDs, the latter is a faster type and can give a boost to the OS and apps. You need 2 thing:
- the bay that holds the factory's HD must be replaced with one that has a socket (and related data and power supply connector to the MB) for a PCIe SSD (you're MacMini doesn't). Apple doesn't sell this. You can have it only via replament if you purchased the Fusion model. So you must be sufficiently lucky to get it from the web as I did (the Bay).
- a PCIe SSD. This is the hot matter. Looks that PCIe SSDs for MacMinis must be Apple firmware flashed. I Bought a 64 Gbyte SSD from a MacBook Air but the firmware can't see it. Where is the problem? Frankly I don't know as somebosy in the iFixit forum states he put a standard Samsung PCIe SSD and works. I asked him detail avout the SSD. I'm still waiting for a reply.
Simon
Это хороший вопрос?
@Simon - Not sure I follow you here. You don't want to create a dual SSD Fusion drive! There's really no point and besides the system won't be any faster. What you want to do here is prep the blade SSD as a bootable drive and place your apps on it leaving the other SATA III (6.0 Mb/s) drive as your data drive.
Depending on your exact model you can't swap out the SATA cable for the PCIe blade drive cable as the interfaces are not the same. If you have a model that has the PCIe blade drive support (with or without a SSD mounted) only they have the ability to support the PCIe SSD blade drive, and only the Apple Retina series PCIe 2 Lane SSD will work in the system (only its firmware is compatible). The newer PCIe 4 Lane SSD's will not work. If your system is missing the cable you'll need to make sure you get the correct cable (SATA or PCIe) for the second drive port depending on the model you have.
из Dan