What is the longest ballad documented through recorded performance by a singer who carried the song as an oral tradition, or family tradition?

I know there are a few immensely long ballads that have been recorded by "literary" singers, wonderful things, but I'm curious about the depth of family and regional tradition, the power of memory and tradition that has been independent, to some small or large extent, from the written word. I'm familiar with many field recordings, but certainly haven't heard them all, so what MOST FORMIDABLE pieces have come through time, riding in the memories of a chain of singers? Those of broadside origin, included, of course.

And, who was the singer?