You can find the answer and additional advice here: http://www.netzspezialist.de/blog/2016/05/23/windows-10-on-hp-z620/
You have to install the drivers from Intel for C602 chipset: https://downloadcenter.intel.com/download/23257/Intel-RSTe-AHCI-SCU-Software-RAID-driver-for-Windows...
Kind regards