My male, Bruno is 75 pounds and 10 months old and he gets about 5 cups a day. He has a fairly high level activity each day but because of his age and activity level, looks thin. I constantly hear comments about why I'm not feeding enough but always from people who don't understand the breed and how they're supposed to look while young so it's in one ear and out the other. I adjust more or less on activity level and if they're knocking their bowls around for more after licking it clean or whether or not there's extra left over when they walk away.
Like everyone else says, it's dependent on several factors, activity level, current weight, and such. I CAN tell you that 2 cups all day is FAR TOO LITTLE for an 8 month old GSD. I would really think about what you're feeding sounds about right. 2 cups a day will get you a dog that's starving all the time.
Speak softly and own a big, mean German Shepherd.