PowerProtect DD6400 Capacity Problem

Dear Dell Support Team,  

I have question about out to inquire about the storage capacity of our Data Domain 6400 system. We have a license for 104 TB , but the system seems to be providing only 90 TB of usable space. The unit is equipped with 23 Disk, each with a capacity of 8 TB, summing up to a raw capacity of 184 TB. Could you please clarify why there is a discrepancy between the licensed capacity, the usable space provided, and the total raw capacity? Are there any system reserves or configurations that might be consuming the additional space?  
Thank you for your assistance.