How to define a storage pool into Load balanced backup method

Hi

I am really new to HP Data Protector , and currently took over a backup project from ex employee.

We have a device example

MSL001

and it has 2 drive

MSL001_d1

MSL001_d2

and From Backup - > Backup Jon- > Description -> I can see its saying "Load Balanced"

But what I dont undersand, How are you defining a storage pool to a specifiq backup with this "Load Balanced" Method,

to be more specifiq - : I was checking couple of Backup  under BAckup Specification -> options -> Select the drive -> click Properties -> Media pool -> No medial pool seclected.

But I can see its going to one of medial pool we have ( currently we have 3 medial pool)

so instead of "no medial pool selected" Hows its going  into one of hte medial pool ??

how does media pool work for Load blanced method ??

Hope it make sense.

Thanks for your help