Door 2L is a full size door on a A321, door 2R is an emergency exit.

Left: http://www.airliners.net/photo/Air-B...211/1414197/L/
Right (same a/c): http://www.airliners.net/photo/Air-B...211/1385742/L/

I remember boarding a Aer Lingus A321 at T1 from door 2L for example.

I think you can get a full size door as customer option for 2R, as it allows more seats (higher emergency exit rating)