In VMWare View you can increase the number of datastores assigned to a desktop pool (essentially the same as a collection). That way if the pool grew because more desktops were required, you could easily increase the amount of storage to support the additional desktops.
It doesn't seem that ability is available in RDS. When using a CSV in a collection it appears you are limited to only one CSV and have no ability to add more if the number of desktops increase beyond what the CSV was originally sized for. Am I seeing things correctly? And if number of desktops do increase, what optons are available? Is the only opton to create another collection?