Currently we have about 20 Mac OS 10.9 MacBook Pros (almost all with SSDs) backing up to individual USB drives. I'd like to consolidate these to one drobo thunderbolt drive array attached to a Mac Mini server (running 10.9 server) using time machine server.

My question is, will this scale to 20 users? Examples I have seen seem to be 5 or 6 users tops, and this isn't easy for me to test (I'd rather not ask everyone to backup to the array and then switch back to USB drives if it brings our network to its knees). My primary concern is saturating our gigabit network, as time machine backs up every hour for every machine, so there would usually be a couple people backing up at any given time. We also have some people occasionally on our 802.11ac network and not on ethernet (usually connected via 802.11n until people upgrade to newer machines), but most of the time people are connected to our thunderbolt displays which have a gigabit ethernet connection on them.

Our network topology is one 32 port gigabit switch with 5 smaller gigabit switches at each desk cluster. The mac mini server is connected directly to the top level switch.

Update: Failing information from someone who has done this in practice, I suppose my question is really around how switches work. If three or four people are backing up simultaneously, and then other two (different) users transfer a file between each other, will they be able to transfer the file at gigabit speeds?