Switch -DS - do not sort archiving files
This switch is meaningful only for solid RAR archives. The compression ratio in solid archives is dependent upon the file order. By default WinRAR sorts files, to be added to a solid archive, by extension. You may disable this sorting using the -ds switch and try to set a more optimal file order. Generally files with similar data should be placed closely together.
WinRAR a -s -ds tools *.com *.exe *.doc *.txt *.*
Files will be added in the following order: *.com, *.exe, *.doc, *.txt, all other file types.
file rarfiles.lst also may be used to define the order of files in solid archives