Why do I Show Less Total Storage Than I Physically Have in my Raid System?
Why RAID Shows Less Total Storage
The reason it shows less total storage than what is physically in the RAID system is because some parts of the drives need to be used for redundancy in case of drive failure. Parity data must be stored for data redundancy to be created properly, ultimately causing some usage from the total storage amount in the RAID system.
Explanation of the different types of RAIDs and RAID calculator: https://www.westerndigital.com/solutions/raid