So, I've bought an used late 2012 mac mini. It came with the original 500gb mechanical drive and an aftermarket samsung 840 evo, 250gb.
Yosemite was installed, and the drives seen as fusion drive. The system was affected by spare errors (attempts to continuously recover keychains, etc..).
I performed an NVRAM reset and splitted the two drives via the usual terminal commands, and installed Yosemite on the newly formatted 840 evo, Internet installation. Installation succeeded, and system rebooted, BUT with no luck: it entered in the efi boot menu. Rebooting with command pressed (boot menu), the machine doesn't even see the installation partition on the ssd.
I tried to install osx on the machanical drive, but again with no luck: disk utility shows it as locked, impossible to unmount.
So my questions are essentially three:
Why my system installs osx on the ssd with no errors, but doesn't see the installation?
Why the mechanical drive is locked?
It is possible that my mini hardware is failed?