Just found this here:
http://blog.macsales.com/15619-special-note-for-adding-an-ssd-to-a-2012-mac-mini
No matter which method you use, once you have both an SSD and a platter-based drive installed in your Mac mini, you should not use the Disk Utility in your Recovery Partition on those drives; it will see those drives as a broken Fusion array and try to repair it, destroying your data in the process.
So that leaves the question how to replace what's in the recovery partition with something more appropriate for this purpose.
http://blog.macsales.com/15619-special-note-for-adding-an-ssd-to-a-2012-mac-mini
No matter which method you use, once you have both an SSD and a platter-based drive installed in your Mac mini, you should not use the Disk Utility in your Recovery Partition on those drives; it will see those drives as a broken Fusion array and try to repair it, destroying your data in the process.
So that leaves the question how to replace what's in the recovery partition with something more appropriate for this purpose.