Well, apparently I figured out how it works.
I see that status.dpn displays a %Full value of ~ 57%. This number can never exceed the value equal to the disk read-only parameter which should never be higher than 65%).
Using the values above I have 57/65 ~ 89%
So, it seems that the situation I have is normal. Could anybody confirm this assumption please?
If so, %Full value of 57% is represented the proportion of actual physical space, i.e., used space is 23,3 TB * 57% = 13,3 TB
How to figure out what part of this used space is used for client backups and what for the rest?