Because VDO is thin provisioned, the file system and applications will only see the logical space in use and will not be aware of the actual physical space available. Scripting should be used to monitor the actual available space and generate an alert if use exceeds a threshold: for example, when the file system is 80% full.
VDO space usage and efficiency can be monitored using the vdostats utility:
Device 1K-blocks Used Available Use% Space saving%
/dev/mapper/node1osd1 926.5G 21.0G 905.5G 2% 73%
/dev/mapper/node1osd2 926.5G 28.2G 898.3G 3% 64%