I have created a test lab in Esxi.
Installed FreeNAS, added 4x 4GB hdd and try to make new pool on Raidz2.
New pool created but the size is incorreclty displayed.
The size displayed in UI is 3.5 GiB, but when I go to the console and input zpool list, I see the correct size of 7.48 GB or 6.96GiB. (see attachment)