Options to investigate if using rar to back up a system:

Commands:

u Update files in an archive

Switches:

-ac Clear archive bit
-ao Add files with archive bit set
Example: rar a -r -ac -ao f:backup c:\*.*

-b Make .bak of archive before modifying it

-r recurse subdirectories

-rr add recovery record

-x exclude file, ex: -x*.bak or -xfoofile.*