CentOS 6.3 BackingStore

[Fogist]

Hello,
I have some problem with video driver "vboxvideo".
My OS is CentOS6.3. 64 bit

I can't set option "BackingStore"

in /etc/xorg.conf :
Section "Device"
Identifier "Card0"
Driver "vboxvideo"
BusID "PCI:0:2:0"
Option "BackingStore" "True"
EndSection

But #xdpyinfo |grep backin :
options: backing-store NO, save-unders NO


What is wrong ?