For my understanding, I need to clone the mail fossil src site first to get a local fossil sqlite database(mytest.fsl) and then open  up mytest.fsl into a local source directory tree. 

For a big fossil site at the size of 10G, it will quickly used up the disk space, since clone part take 10G and check out take another 10G.

I am hoping fossil can provide a better way to resolve above challenge.

This request is purely from end user point of view.

Support "fossil co http://myfossil.test.net/srcdir/subdir2"