[citation][nom]LuckyDucky7[/nom]Looks to me like it's Drive Extender from Windows Home Server, just tweaked a bit.[/citation]
That was exactly my first thought. That sounds like DE at heart, with a twitch of Greyhole in it for good measure (DE was limited to one copy, GH allows at least three).
I do wonder if they use the 1st-gen DE implementation or the 2nd-gen (only on VAIL betas) one: the VAIL implementation took an extra 20% hit compared to WHSv1, but it allowed for error/consistency checking in the pooled data.
As for how it works, it's rather simple: the maximum pool size (that is, how much data can be fitted into the "Storage Space") is the sum of the reserved HDD space (so, with a 3-copy Storage Space and 1GB reserved for each disk, it would show as 3GB total storage), actual usable space would be 1GB (or 800MB, if they're using the 2nd-gen implementation of the DE engine), and used space would be shown as 3 times the actual data put into it (so, a 50MB file would report as 150MB used).
This, however, seems to be an early implementation. Showing all available space made sense in WHSv1, since all drives were pooled together and you chose to duplicate them or not; but as Storage Spaces are in fact "mini" DE implementations with duplication always enabled, Microsoft might want to simplify how storage area is shown, so as not to cause confusion (as it seems to be causing right now).
Cheers.
Miguel