What fraction of the members of the Rajya Sabha retires after every two years?

Rajya Sabha is a permanent House that is never dissolved. Each member serves a term of six years, and one-third of the members retire every second year, with elections held to fill the vacancies. This gives continuity in the upper house. One-half would imply a term of four years, and one-fourth or one-fifth do not match a six-year cycle divided into two-year steps.