Hey all, a few questions on btrfs

I'm in the process of building a btrfs storage server (mostly for evaluation) and I'm trying to understand the COW system. As I understand it no data is over written when file X is changed ot file Y is created, but what happens when you get to the end of your disk?
Say you write files X1, X2, ... Xn which fills up your disk. You then delete X1 through Xn-1, does the disk space actually free up? How does this affect the 30 second snapshot mechanism and all the roll back stuff?

Second, the raid functionality works at the filesystem block level rather than the device block level. Ok cool, so "raid 1" is creating two copies of every block and sticking each copy on a different device instead of block mirroring over multipul devices. So you can have a "raid 1" in 3, 5, or n disks. If I understand that correctly then you should be able to lose a single disk out of a raid 1 and still have all your data where lossing two disks may kill off data. Is that right? Is there a good rundown on "raid" levels in btrfs somewhere?

Thanks all.