I have some problems with disk performance. I have 6 x WD 500Gb RE4 disks. Each disk gives 135Mb/sec throughput. All measurements are made with hdparm with options "-tT" (I know that it is just synthetic test, but I need some start point to make measurements).

I have controller with Sil3124 x 4 ports PCI Express 1x

So...

1. RAID0 on controller with 2 disks gives 200Mb/s - ok, pcie limit.
2. RAID0 on motherboard with 2 disks gives 270Mb/s - niceeee :)
3. RAID0 on contorller with 4 disks gives 200Mb/s - ok, pcie limit.
4. RAID0 on controller with 4 disks + 1 disks on motherboard = 340Mb/s ... :(
5. RAID0 on controller with 4 disks + 2 disks on motherboard = 300Mb/s .... why? Any ideas? Maybe need more cpu power?

Now there is Pentium D Dual core 2.8Ghz, 4Gb RAM. It is dedicated box for storage.. no other activity.