I read this claim inIn the Icebreaker series by Viktor Suvorov. In the books, he says that at the beginning of World War 2, the Soviet Union had roughly 7 times as muchmany tanks as Nazi Germany, which had 3000-4000 tanks.
I can't remember the exact figures, but according to him the Soviet Union had between 2000020,000-3000030,000 tanks (I will edit if someone can point out the exact figures in his claim).