lzo files conundrum

[Renato Gallo]

Hello, 

we have two machines same system 100 Gb of virtual disk both have the disks on a zfspool. 
from the df -h point of view the disks use is quite similar. 
we backup those machine regularly during the weekend using the scheduled backup of proxmox from the datastore menu. 
we cannot understand why one machine have a .lzo file of 9.something gigas and the other has a backup .lzo file of around 40 gigas. 
can you explain this to us ? 

Renato Gallo