In each of 2 very large bowls, layer the cabbage with the salt. Let stand for 45 minutes. Toss the cabbage well and let stand for 45 minutes longer.
Fill a sink with cold water. Swirl the cabbage in it to remove the salt; drain and repeat. Drain the cabbage well, lightly pat dry with paper towels, and transfer to a very large bowl.
In a mini food processor, combine the garlic, onion, ginger, and sugar; process until pureed. Add the fish sauce and process until blended.
Add the daikon and scallions to the cabbage and toss. Add the garlic mixture and the red pepper powder; toss thoroughly. Pack the cabbage into three 1-quart jars. Press plastic wrap on the surface of the kimchi and put the caps on loosely. Let stand at room temperature for 3 days, until the cabbage is tangy and bubbling. Store in the refrigerator.
