Two types of reels are used for carp fishing, ‘’Baitrunner’’ reel or front drag reel (big pit).

Regarding the Baitrunner it is a reel with two brakes, a fighting one and a brake that can let go bait without resistance. This type of reel is also used by fishermen surf casting.
http://cgemery.com/reels/spinning-reels/emery-trident-spinning-reel

The reels with front drag have a great line reserve and should be used with a loosen brake . Following a touch the fisherman must slow the spool with the palm of is hand and then apply the brake for the fight.
http://cgemery.com/reels/spinning-reels/emery-long-cast-spinning-reel

Some people swear only by the Baitrunner and for other it's the big pit and nothing else. Each one has its advantage and disadvantage, it is simply to find the best one for you.