Big problem with PERC H200 performance

I have a T110 II with PERC H200 and two 500G SAS 7200rpm HD. When I got the machine, I set the HDs as RAID1. it took 12 hrs or more to initialize. I thought it was normal until recently.

I used HD testing software yesterday to see the performance, and I got a very poor result. The reading and writing speed are only aroung 35-40 MB/s. I also ran the test on my old desktop with an old SATA HD and got the result with 100+ MB/s.

It caused some problems. For example, the server would be held when the HD I/O was high, or it took a very long time when I tried to make a new big file. Does anyone know where the problem is? Please help me. Thank you very much.

Add some info.

In the H200 Bios setting, the status is "optimal". I also used Dell's DEST to see how's going on, and I got the picture below. The red part was the status in windows. How does that happen?