. Installation :

Each host is installed with the node iso.
Harddrive are not SSD and are in RAID5 (physical or logical)
Each harddrive has a standard oVirt node install auto partitionning,
except for one thing, we reduce the / mount point to make a new
partition in XFS for the data storage mount point (the partition is
inside LVM in our case)

. The problem :

We experienced on all of this hosts huge discrepancy between the LVS
command and DF on usage of the different partition. (sometimes up to a
90% difference !)
Spoiler alert, DF is right, LVM is wrong.
I think (but i might be wrong), that when we delete -in ovirt- a lot of
data on the drive, LVM doesn't get all the data about that.