Stated Capacity vs. Actual Capacity

Hi all,

New to this forum, so forgive me if I’m asking a redundant question…I did search to see if I could find an answer before posting.

I recently bought an EX4100, equipped with four WD Red 6 TB Hard Drives. This is sold as 24TB capacity, but when I installed it, my computer sees just over 16TB available. I understand that some headroom is necessary for various functions, but it surprised me that 25 percent of the total capacity is being gobbled up that way.

I have the unit attached to a PC running Windows 10 Home, v1903. I have one volume, set up on RAID 5, with a listed capacity of 17.91.

Is that just the way it is, or are there ways I can access additional capacity?

And, down the line, what’s the maximum size of Hard Drives this unit will support should I need additional capacity?

Thanks in advance!