bttrfs questions

So it seems the best way of getting Raid1, for the purpose of protecting your data if one hard disk fails, is to use Software Raid, and then put bttrfs on top? Is this correct? Is it ok to run bttrfs in a VM using virtualized disk? I have heard people say you shouldn't do this, because there is no guarantee that data has been written to physical disk when requested by the VM. Is this correct? Overly paranoid?