Maybe you happened to get a unit with a faulty disk controller...
Well I downloaded Window Server R2 2012 Essentials (180 day trial) and used "intelligent Provisioning.
Set to use Raid controller
Installed on DVD SATA slot (bay 5)
It all installed OK - except I don't understand how it works! And it seems you have to use a domain to share - which Win 7 HP and Win 10 upgrade don't support! So I don't see how I can use it anyway?
Looking at the drivers they are identical to the ones installed for Win 7.
First impressions - same issue - but I have "cleaned" 1 x 3TB drive in DISKPART - inserted it - deleted array - remade array - made a new volume - formatted it. copied a few GB across - OK. It's now sitting there doing nothing!
Soak test underway. Going to Gym to hit something!
If this fails - it's going back! (with an assumed faulty disk controller)
Mel