This VPS server is showing that the machine has 417.45GB disk space: http://puu.sh/UT9n
Here's the results of df -h and mount: http://puu.sh/UT9N
Here's mtab: http://puu.sh/UT9Y
The VPS should have 600GB disk space.
What could this be?
You need to ask your VPS provider - because both Webmin and df show that the total disk space is ~418 GB.
The discrepancy in space used is because Webmin counts space reserved for the root user.