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
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