Drainboards can be created on one or both sides.
Prep sinks come in various shapes and sizes. This D configuration is a good choice and often overlooked. What makes sense to me is that it’s wider in front — where the action tends to be when you’re peeling, cutting and cleaning.
Runnels, or channels in countertop, are not often seen around a prep sink. This one, photographed in a Clive Christian kitchen, is large enough to warrant them and to anchor a Samuel Heath bridge faucet as well. In this case, the D sink is undermounted with a neutral (or no) reveal — which means that the counter and the inside edge are flush. When vegetables are rinsed and put on the runnels to drain, or if drippy things are removed from the refrigerator, they go directly into the sink.
Prep sinks are often squeezed onto corners or put on the end of an island where they don’t take up much space. My preference is to locate a prep sink near the refrigerator so it does double-duty for draining, thawing or other chores as well. Adding runnels is a bonus.