I've noticed that vusagec calculates space based on file size, but it is
prone to errors in case it needs to calculate many emails that are
smaller than block size.
In case file size is smaller than block size file system will use e.g.
4KB for that file and vusagec will calculate real size. In my example
file system is giving me 230 GB used space and vusagec gives me 100GB
used space. It is huge error in my opinion.