I used to have an HP MediaSmart Home Server and I absolutely LOVED that you could add and remove drives as needed, and it would automatically handle balancing and selective folder duplication.
Well, I purchased one of those tiny Intel NUC computers (NUC6I5SYH) (it rocks, by the way with it's i5 and SSD!) along with a Mediasonic 4 Bay SATA HDD Enclosure. The enclosure is populated with 2 x 2 TB drives and 2 x 1 TB drives. One of the 2 TB drives and one of the 1 TB drives each have tons of media and other files. The other two drives were empty.
So last night, I installed DrivePool, and after a little bit of testing to better understand how it works, I created a new pool, and added all 4 drives. I then used the slick "copy everything into the hidden folder" trick to quickly populate the pool, I configured the settings to enable duplication, and i then clicked "re measure". Today, it completed. Everything is balanced and duplicated.
I then removed the drive letters from the pool member drives (so Windows Explorer is now clean) and mounted the member drives as folders in a folder on the new DrivePool drive for "just in case" times when I want to look into the member drives directly.
I tried to get Storage Spaces working under Windows 10, but it failed in two ways: First, it requires that all pooled drives be erased. This makes the process very, VERY long. And second, for some reason, Storage Spaces simply wouldn't work with my drive enclosure.
In the end, I'm very, VERY happy with DrivePool. Now to test out DriveScan and put it through its paces. Looks like StableBit will be getting some of my money! HIGHLY RECOMMENDED!