I have the same problem!
I have 2 RAID (1-ssd, 2-hdd).
mobo --- ASUS Gryphon Z87.(raid rom 13.5.0.2.2164)
hdd --- 2x SanDisk Ultra Plus 128GB [Raid1] + 2x WD4000FYYZ [Raid1].
At the same time, on the ssd array I got acceleration reading, and on the HDD array - no!
HDD RAID 1
SSD RAID 1
As can be seen, raid 1 on ssd works as it should and gives almost a x2 read speed compared to 1 ssd. But with hdd - No!
Tested on multiple platforms (z77, z87, z97) - everywhere raid 1 does not work correctly with hdd, but ssd -works fine (that is, the array gain in reading speed !!)
The same situation with an array in HP proliant mickoserver gen 8 server (has renamed intel controller).
Here is a test of the old disks (80GB) in raid 1 and raid 0 + ASUS Gryphon Z87.(raid rom 13.5.0.2.2164):
RAID 1
RAID 0
As we see the increase in reading speed of RAID 0 was almost 2x faster, while RAID 1 - reading speed at 1 disc.
From the tests carried out by me, we can conclude that the controllers in the intel chipsets with support raid 1 do not work properlywithHDD drives!