In boiling water, cook the carrots for 3 to 5 minutes until tender. Drain and set aside. Boil the beets for 8 to 12 minutes until tender. Drain, peel, chop into small cubes and set aside. Boil potatoes in their jackets until tender but slightly firm (about 20 to 30 minutes). Drain, peel and cut into small cubes.
In a large bowl, combine cubed potatoes, carrots and beets. Add chopped onion, pickles and herring. Mix well.
In a small mixing bowl, combine sour cream, mayonnaise, mustard, sugar, vinegar and stir to mix well. Add this dressing to the potato mixture toss well to mix thoroughly. Garnish with chopped parsley and sliced boiled eggs. Refrigerate for several hours (preferably overnight) before serving.