Disk selection in device pool

My storage pool containing 3x2TB disks shows as Disk A being full with 0 left. Which is fine, I expected that. However I also expected that rather then throw me countless erros ~ that BE would simply just 'carry on' using Disk B and then when that's full, Disk C and so on. As by the time Disk C would become full - data would be expired/recycled from Disk A / I think you get the idea.

How can I make BE behave in such way? I don't seem to be able to edit anything with the storage pool itself.