Hi Dan, thank you for helping. Actually, the "few years" system was refering to the SSD, the Mac Mini is brand new.
Actually I had the answer from OCZ support :
The issue is incompatibility between the older SandForce 1222 controller used in the Vertex 2 and the newer Intel Haswell platform used in the Late 2014 Mac Mini. The incompatibility started with the Intel 8 and now 9 series chipsets and spans across all products that used the controller regardless of manufacturer. It is expected behavior to be able to connect the Vertex 2 then clone to it, but if you try and cold boot to it the detection will fail. Unfortunately, the Vertex 2 and the controller it utilized are long EOL and never received a firmware update (if that was even possible) to adjust for the release of these new chipsets.
So I can stop looking around it simply wont boot, ever. Product being End Of Support, no new firmware will ever fix this.
So I guess, i'll have to look another SSD. Hope this can help other.