The third and last volume of the biography was released last year in Germany and an English translation is about to appear early this year. The first volume is from 2006 and the New York Times had a review back then:
> Indeed, this book, the first of a projected three
> volumes, seems to be written not by a scholar and
> editor named Reiner Stach but by a Kafka character
> called, to borrow the words of the book's promotional
> materials, "the definitive biographer." [1]
[1] http://www.nytimes.com/2006/01/01/books/review/01roth.html?p...EDIT for those with paywall issues:
If you are interested in the Kafka biography by Reiner Stach which the original post seems to promote you are better off reading the NYT article I linked above.
If you are interested in the Kafka pieces from the original they are also published in the kakfkaest blog [2]. I'm unsure if they are published with permission though, given they even misspelled "Reiner".