I just purchased a strix x99 mobo for a new build with a i7 6950x. On a clean install of windows to a M.2 SSD I took 2x2TB WD red drives from my old build that were in RAID 0 and put them into the new system. With the BIOS in RAID mode I booted up and initialized the disk and mounted it as my 😧 drive. However it was SLOW. I ran a benchmark and the read speed was 12MBps. in the old system it was ~ 900MBps they are connected to SATA ports 1&2, I have 2 more SATA SSDs and an optical drive connected to other SATA ports and they all work fine.

I made sure I had the latest BIOS flashed and the latest intel RST driver installed and it was still slow. Task manager also shows disk usage at 100%,. after poking around online I tried all the fixes such as disabling windows 10 notifications, disabling MSI for the AHCI controller, etc and nothing helped. I also moved the pagefile to the RAID array but while troubleshooting moved it off the array, set to manual size, nothing helped. I decided to boot from my old win 10 ssd which was working fine yesterday in my old machine. Even then the RAID array was slow and stuck at 100% usage, this makes me think this is an issue with the motherboard. Has anyone else encountered this situation or know how to fix it?

I reached out to Asus customer support last night but I need this fixed quickly as I use this machine for work and I don't really want to rebuild my old machine after dropping so much money on a much faster new one.

When I get home I'm going to put some old SATA II drives in RAID 0 to see if they have the same issue.

ninja edit: old config that the array worked fine on was an Asus rampage IV extreme and Intel i7 3930k with 24GB RAM

System:
Intel i7 6950x
Asus Strux x99 mobo
64GB Corsair vengeance LPX 2133mhz
HIS R9 280x GPU
Samsung 950 pro NVMe 512GB M.2 SSD
2x 2TB Western Digital Red 2TB in RAID 0
Corsair AX 760 watt PSU