I'm doing a new install, and everything seems to have gone fine apart from the incredible amount of time it's taken.
It does have 6 x 4TB drives in RAID6 and I am installing from a USB DVD drive as I had no SATA ports left, but this is getting rediculous.
Maybe you could try a network install and only use the USB DVD to boot. I remember similar issues while installing servers using remote iso to install via USB drive emulation with the servers management hardware.
Regards, Simon