How Does the Media Server Load balancing works?

Hello,

I was trying to finger out how the media server load balancing works. I have a fell sug's configured on our environment. But here comes the question:

If I set just one storage unit for a sug,  Will the jobs be balanced using the storage unit configuration? (We can pick all the medias servers, selecting : Only use the following media servers from Storage unit's tab)

or

I must have to pick at least 2 storage units for a proper sug configuartion.

Thanks in advance.