Poweredge r620 with perc h710 mini poor performance/problems

Hey there!
I have an Dell Poweredge r620 with an perc h710 mini as an raidcontroller.

The Server is equiped with 8x 600gb 10k SAS HDD's, 1x 1tb Crucial MX 500 SSD and another 1x 500gb Crucial MX 500 SSD. || Raids:1x RAID 5 with 8x 600gb 10k SAS HDD's | 1x RAID 0 with the 1tb Crucial SSD | (((1x RAID 0 with the other 500gb SSD)))

The 500gb SSD strangely randomly dissapeared one-day with the error-message "Disk 9 in Backplane 1 of Integrated RAID Controller 1 is removed", a few days later, however, it was recognized again, and it was determined that it was still 100% write-stable. <= This is silly, but not my biggest problem...

As soon as something is written to the other 1tb SSD the server has an iowait of 50+ and is only barely usable, in addition, the SSD is very very slow;
1gb write:
root@iotest:~# dd if=/dev/zero of=/root/testfile bs=1G count=1 oflag=dsync
1+0 records in
1+0 records out
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 50.8903 s, 21.1 MB/s
2gb write:
root@iotest:~# dd if=/dev/zero of=/root/testfile bs=2G count=1 oflag=dsync
0+1 records in
0+1 records out
2147479552 bytes (2.1 GB, 2.0 GiB) copied, 170.887 s, 12.6 MB/s

io-wait during the test:
2021-11-21 19:09:58 (0:01:18) - CRITICAL on CPU_IOWAIT (Min:7.2 Mean:43.0 Max:57.7): bash, io_wqe_worker-0, pvestatd

Here are some pictures of the configuration from the Raid-Controller etc (I hope you can understand what it says since it is in German :)).:

Controller-Properties:

RAID5 - HDD01 - Properties:

RAID0 - SSD01 - Properties:



I would be very grateful if you could help me.

Kind regards;
f.nmann