If you are a new disk and wiping them to setup a DIY Fusion disk, how does the Mini carry on working afterwards... haven't you just wiped the OS? Without an optical drive, how can you clean the disks and still be able to reinstall an OS?
You could also try
To do this boot your Mac while holding option+command+R Then when it loads (takes about 5 mins) go to
disk utility and format your drive. After you have done that go back and select the option
Reinstall OS X.
Hope this helps.
Without an optical drive, how can you clean the disks and still be able to reinstall an OS?
Simplest and cheapest way:
create a bootable volume from the OS X Installer on a USB Stick.
2 days ago I used the (free) DiskMakerX to clone the
10.10.3 OS X Installer (it works also with older OS X versions) from
AppStore to a
USB Stick and used that bootable clone to start from it and install
OS X on another volume. Everything worked fine.
This guide explains how to create a bootable USB installer, from the installer you'll be able to wipe the internal disk through disk utility before installation
I have been able to use OS X purchases from my App Store and use for clean install. Assuming you have gotten updates since lion was released? Go to your purchases and option + click the OS you want installed. The limit is naturally set so you cannot load an OS older then your machine.