The high pile shag carpet, often make by Shaw, Tufftex (Tuff Tex), Sutton, CabinCrafts, Couture and Queen, and others and is known as Shaggy Sheik, Casabella, and Peilcan Hill II and more.
The tufts are about 3/8" in diameter and about 3/8" apart from each other and about 2.5" long (other varieties vary). This carpet is too thick to use a roller beater brush on and one shouldn't be used for the carpet's own protection (just ask the manufacturer).
So how do you clean a high pile shag carpet? Use this awesome new tool which actually rakes the carpet while it sucks from the center of two rows of long, stiff, plastic wire fingers. This tool is also called "Rug Tool with Tines". It will help loosen the debris and suck it out of the carpet! In fact many of these long carpet manufacturers recommend "the use of a suction only vacuum for pile construction that is sensitive to brushing or rubbing [by beater brushes]".