How can you wipe and reinstall OSX on a Mac Mini (which has no optical drive)? 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?
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.