Is it possible to install two 2.5" drives in 2014 Mac Mini?

@ewhizz - The 2011 and 2012 units have dual SATA ports so they could be setup in a RAID.

The 2014 is a bit different here we have a tortoise and a hare problem!

The slower SATA port - SATA III (6.0 Gb/s) and then we either have a AHCI drive or a NVMe SSD drive. And to add more confusion we have the older Sierra release which has RAID support and the newer High Sierra and onwards which don't natively $$ from a third party.

Frankly, Using a single SATA SSD in this series is about the best you can get. Adding a second drive only makes sense if you have run out of space on the first or you want a bit more performance from your old spinning rust drive setting up a Fusion Drive with a small SSD.

@danj Sure, but the "Because of the I/O speed difference you can't RAID the drives." comment is not correct. Setting up a RAID with dissimilar drives is not ideal, perhaps, but still very possible.

RAID support remains beyond Sierra in High Sierra, Mojave etc — the controls have just been removed in the GUI based Disk Utility.app. The ability to manipulate RAID volumes (AppleRAID) is still available via the command line diskutil

Given that 'RAID' covers striping, mirroring and concatenation, using two different disks is still possible.

@ewhizz - Yes RAID covers many variations! But you risk or lose when you try to matchup a mismatch of drives. I/O will bite you if your data move is bigger and faster than what the other drive can support (software RAID will slow the write or read to the slower drive loosing performance and hardware will bomb out). In a Mirror set the larger drive is trimmed to be equal to the smaller wasting the other space, and lastly recovery of data is not really possible in any RAID set which only has 2 drives. This is more an issue when you have a HDD vs SSD setup.

Bottomline: They all require equal drives & I/0 to be dependable.

What I think you are saying is Just a Bunch of Disks - JBOD that is quite possible! That way the two drives are seen as one! But then you get into what the file sits, is it on the fast or slow drive. It also won't protect your data!

Basically, I would just use each drive independently and manually controlling where things sit. People are still smarter than computers!