The idea in my mind is because some part of my web application does not work functional under apache with mono,but fine under xsp2.I stuck in this problem for a week.May be the problem is permission.Can I just run xsp2 instead of apache? If I can,what problems will happens? Thanks.
You can use xsp instead of mod_mono or fast-cgi, and it'll run fine. There are however some limitations which may be important to you - XSP only supports HTTP 1.0 and it's not as configurable as either of the other options. If you're really stuck running the site under XSP then you might want to consider proxying it, perhaps through Apache mod_proxy or Nginx or Varnish. See this Stack Overflow question on what you'd be missing by not having HTTP 1.1.