I have an Asus P8Z77-V PRO. I have five 2TB drives connected. Two are on the Z77 6 Gbps ports and three are on the Z77 3 Gbps ports.
I created a RAID5 array in the RAID BIOS. The volume status is "Initializing". It's been like that for over 12 hours.
How long should this take?
It may take a while taking in consideration the size of the Hard Drives however; you should be able to install the Operating System in the meantime. It is not necessary to wait until the initialization is complete, you can install the Operating System in the meantime.
If after you install the Operating System the system is still initializing then leave the computer overnight within the Operating System.