Poor performance on RAID5

Hi all,
First of all let me thank this community for teaching me a lot throughout the years. This is really a very useful forum.

I own a Gigabyte GA-965P-DQ6 with an ICH8R southbrige, I’m using a modified BIOS with ROM 8.5.0.1030 and driver version 13.2.4.1000

Recently I changed my old configuration which consisted of 3x 320GB HDDs to 4x 500GB, I proceed to build two raid arrays, one RAID0 and one RAID5 using the same 4 hdds, similarly to what I already had on my old configuration, however I’m noticing a drop in performance on the new RAID5 Array.

Using HDTune I measured the Reading speeds to be around 100MB/s (which is not so bad) but the Writting speeds are below 50MB/s max and average around 15MB/s
I’ve noticed that disabling caching actually improved performance slightly which for me is a little bit strange…

All HDDs were thoroughly tested individually and are working fine so I know this isn’t caused by a failure of any of the disks.

Is this normal?
Could it be that 4 disks are too much for this controller to handle properly? Would I benefit from a driver change or is there something else I should try?

Thanks in advance and regards.

This is not the best Intel RAID ROM/Driver combination. If I were you, I would update the Intel RAID ROM and "downgrade" the Intel RST Driver to the v11.2 series ones.

That is not a good idea. Different RAID arrays should have different members (HDDs/SSDs).