I have read it several times and it is helpful but unfortunately it doesn't discuss using multiple drives.  In that guide they are just using one drive (sdb) in each host, my confusion revolves around how to make use of the second drive I have in each host. 

For example if I left all three devices as SDB then my second hard drive SDA would never be used.  So if I throw SDA in there say for the data volume does that mean I can only use up to the amount of available space on SDA disk for data storage? 

My main goal here is that I don't want my main data volume to be limited to the available space of a single drive.  I want to make best use of the 2x2TB drives I have in each host.  If I chose "sda" device for my data volume that device only has 2TB.