Where is my space?

Hello.

I have a problem with pool capacity presented to hyper-v hosts

I got recently installed and configured new PowerVault ME4024 storage with 12 SAS SSD 960GB and 12 SAS HDD 1,2TB.
I've created 2 disk groups: 1-st with all SSD's and 2-nd with all HDD's.
Each RAID6 with dedicated hot spare. So total capacity should be around ((12-2-1)*1,2+(12-2-1)*0,96) 19,44TB
Then I've created pool of these two disk groups, and then a volume from that pool (full size).
The volume shows total capacity of 19,3TB just as it should.
But when I presented this pool to a hyper-v host (Win Srv 2019 Core) it shows 17,6TB capacity

So there's 1,7TB missed somewhere. But where?...