i found the problem.
The kernel version in Centos 7.8 with version 3.x.x is really too old and does not know
how to handle fine new SSD disks or RAID Controllers with latest BIOS Updates applied.
Booting and Archlinux latest iso image with kernel 5.7.6 or a Centos 8.2 with kernel 4.18
increased the performance at the right values.
I run multiple dd tests on the above images using bs of 10, 100 and 1000M and had
aconstant write speed of 1.1GB/s.This is the expected value for 2 SSD in RAID 0.
I had also enabled cache settings on the Dell Perc 710 Raid controller : Write Cache set
to "Write Back", disk cache set to "Enabled", read cache to "Read
Ahead".For those who think "Write back" is a problem and the data might be
corrupted, this should be ok now with the latest filesystem xfs or ext4 , that can recover
in case of power loss.To make data safer, i also have a Raid cache battery and UPS
redundancy.
Now i know i must run ovirt 4.4 with Centos 8.2 for good performance.
I saw that Upgrading from 4.3 to 4.4 is not an easy task, multiple fails and not quite
straight forward(i also have hosted engine on the shared Gluster Storage which makes this
ipgrade even more difficult), but eventually i think i can get it running.
Thanks,
Emy