Chana dal on the left, yellow split peas on the right. Notice how the yello split peas look like spheres that are cut in half. Chana dal are more of a rounded cylinder. Chana dal also have a more rippled appearance to the split pea's smooth surface.
Yellow split peas and Chana Dal look very similar, and are sometimes sold with the wrong label. But beware- taste and how they cook is different!
Chana dal have a more favorable glycemic index and are apparently a godsend for diabetics. This guy has done a lot of research on the subjet.
Yellow split peas will cook down to mush quite quickly, whereas Chana Dal will hold their shape well.
You can substitute yellow split peas for most curry recipes that use Chana Dal. However the swap won't work as well if the curry is a "dry curry" where you want the dal to keep its shape. If the end product is mashed, pureed or a soupy consistency, the swap won't be as noticable.
I like the taste of Chana Dal much better than yellow split peas- probably mostly due to the improved texture of cooked chana dal.
The best place to buy Chana Dal is at an Indian grocery store- will be in big bags and cheap. I was in a hurry and purchased a smaller bag at a natural foods store but it was more expensive ($4 for the small bag seen up top; Indian stores will give you twice that for the same price). If you are lucky though you might find it in the bulk bins at Whole Foods, generally at a good price.
My favorite Chana Dal recipes: