Change paper format for scrbook class (using package typearea)

Question

I try to use scrbook class, and play with basic options - paper size. I know that is based on KOMA script and for these reasons I should use package typearea instead package geometry. See MNWE:

\documentclass{scrbook}
\usepackage[paper=b4paper]{typearea}

\usepackage{lipsum}

\begin{document}
  \lipsum[2-8]
\end{document}

I got Latex error: Option clash for package typearea! So I try this

\documentclass[paper=b4paper]{scrbook}
%\usepackage[paper=b4paper]{typearea}

\usepackage{lipsum}

\begin{document}
  \lipsum[2-8]
\end{document}

This leads to Latex warning: Unused global option(s): [paper=b4paper]

Answer 1

I've found that KOMA classes don't change the page size if you don't pass the option pagesize.

So the solution should be:

\documentclass[b4paper,pagesize]{scrbook}
\usepackage{lipsum}

\begin{document}
  \lipsum[2-8]
\end{document} 

I suppose that you get that warning because the b4 paper size is not defined in typearea.sty.

Answer 2

According to KOMA-Script manual scrguien.pdf, Section 2.6 - Options and Macros to Influence the Page Layout there is no need to load package typearea with a KOMA-Sript class, since it's including in scrbook, etc.

Also, the syntax of the option for the class wouldn't be paper=b4paper but just b4paper

So the manual would indicate:

\documentclass[b4paper]{scrbook}

\usepackage{lipsum}

\begin{document}
  \lipsum[2-8]
\end{document}