Hi all,
I finally found the cause of my problem.
I did not remember that I had changed the MTU on the bridge ovirtmgmt to 9000 but also on
my NFS server and my switch.
Doing some ping NFS server I realized that I had an issue.
I had to set the MTU to 9020 on my switch (IP header). Right after that change, the
storage domain cam backup properly.
My problem is fixed!
Thanks guys.