create branch from svn repos

Hi All

I have a svn repos with this layout

trunk
tags
branches-- b1
                    b2
                    dir/ b3
                           b4

i used git-svn to clone a svn repos. and i have remote branches like

svn/b1 svn/b2 svn/dir

i can create a local branch from b1 or b2, or even dir with command like git checkout -b local/b1 svn/b1

but if i want to create a local branch for b3 with command git checkout -b local/b1 svn/dir/b3

it will fail with error messages like

fatal: git checkout: updating paths is incompatible with switching branches/forcing Did you intend to checkout 'svn/dir/b3' which can not be resolved as commit?

so is what i want to do feasible?

Thanks!

Ming