[ubuntu] libvirt seven guest verif slow, many disk acces

Hello,
I have problem with my VMs, that are sometime very slow.
When I run VM I have many disk acces.
iotop show me a jbd2/dm-2-8 process that use many io (more than 50%) with only a seven VM powered on.
I didn't succeed installing drivers in my VM because of not signed driver refused.

Could you help me ?

Host :
cpu Intel(R) Core(TM) i7-4790 CPU @ 3.60GHz
16 Go Ram
FakeRaid mode raid 0jbd2/dm-2-8