H755 Raid 4kQ32 slow write speed

Hello!

Can somebody help me about this problem?

I have R550 server with H755 8GB controller. I'm using RAID 5 with 5x Samsung PM1643a 960GB SAS SSD. I know, that are not certified disks, but, I'm using this type a lot other servers (Dell and non Dell also), and theese are working fine.

Why does the 4KQ32 write speed terrible slow? Raid settings: read ahed, write back and disk cache enable. I have tried all option turn on or turn off, the result also the same.

I attached also a non Dell RAID result, same SSD, same RAID, same RAID settings but the 4KQ32 write speed much faster.

Can somebody give me any advice?

Best regards: Péter

Dell_H755_raid

non_Dell_raid