I am sure this is a newbie question, please be patient. 
My OMV has an 80GB boot drive and two NAS 4TB drives as RAID? (4TB available)
I created two Shared Folders a Dads (Private) and a Public.
In Windows 10 these show up as Total Size 3.58 TB with 1.87 TB Available (Each)
1. Is the 1.87 TB available available in each Shared Folder Fixed or does it expand as needed, as files are added?
2. If the 1.87 TB is fixed per Shared Folder, is there a way to reapportion the space, because Dad really doesn't need 1.87TB for family private stuff.
(Not to mention that the Media folder is nearly that big to begin with, but, you buy what you can afford.)
Thanks!