The best preventive traps are the glue ones. You fold them up and they form a glue tunnel. Critter of any size from field mouse to a rat goes in and there it remains.
If you put a normal trap under a raised floor there will be someone missing fingers after they have forgotten it is there and try to run cables. Either that or cables/fiber chopped in half. The glue ones are humane to the human personnel which IMHO is probably more important. You also do not get the mess with poison bait. While rats and mice eat the bait where they find it, squirrels and "edible" doormice* take it somewhere else like on top of a server or NAS grille and eat it there so the crumbs get into the machinery.
I have seen the glue ones sold in Euriope, but not in the UK. If you are setting up a new building make sure you put a few of them in critical places under the raised floor. Replace annually or when they start to stink (you could have guessed by now - I have had to deal with this one).
(*) The edible doormouse is the European vermin from hell - everything a rat does + walk on vertical walls and ceilings and dig tunnels as well as chewing through anything except steel mesh on its way as well