Look at the picture of the upside down clump. For me, the storage roots are the larger tubers and the feeder roots are the thinner roots attached to them. Some can be tiny and reach out two feet or so away from the main clump. I always use water pressure to remove the soil from around the tubers and flush out the smaller feeder roots. I don't know if this really makes a difference but it sounds logical to me. The vendors usually trim the roots for packaging and shipping reasons.
