Taking one of the new entry-level mini Macs and adding a second HDD to it is not the easiest task, but iFixit has slightly reduced the barrier for this modification by launching the Mac Mini Dual Hard Drive Kit, a set of tools that comes out for just US $ 70.
Bringing a screwdriver, screws, shock absorbers and even the necessary SATA cable to install on the incoming Mac mini, this kit is complete. The only thing it does not make the operation simple: the guide showing all the steps of the process, in a total of 38 steps, makes it very clear that this is not for everyone. Not to mention that the type of change that makes your guarantee worth nothing.
Anyway, if you are feeling brave, you already know that you can find all the necessary tools in one place. Now it's up to you to decide which HDD / SSD to install.