This is a well known heirloom paste variety. Semi-determinate vines produce 4″ elongated red fruit, ripening midseason.
2015 – May 20- set out plant. June 28- 4′ thin vine with 6 pointed fruit. July 8- 4′ vine with 8 fruit.
Links:
http://store.tomatofest.com/San_Marzano_p/tf-0443.htm
http://tatianastomatobase.com/wiki/San_Marzano