Sorry, let me try to be more clear.
GUI shows 4.0 TiB total. I'm using 966.1 GiB, so, I should have 4.0TiB-0.966TiB= 3TiB. But GUI showing 2.6 TiB.
Notice that I'm talking about GiB not GB and TiB and not TB. What I mean is that the values are mislabeled. I know that 4x 1TB is only 3,6TB.
And I meant 400GiB or 0.4TiB, not 4GB