Mirror Image...Is it bad for SEO?

If one site has mirror image site...but both are located at different web server...
Let us take an example of site 1 and site2.
-Site 2 is the mirror image of site1.
-SEO process is only for Site 1.
-SEO result for site 1 = ? (if it will show no result after completion of SEO of site 1....because of mirror image of site2)

What is your suggestion?

Is there any tool is available which will tell you that site has mirror image or % of equal ness between two sites?

Yes, it is bad for SEO. Google for example will alternate between listing the first and the second site, and if the second has almost no backlinks, its ranking on the search engine results pages will be much lower.

You can use http://www.copyscape.com to see if a search engine can find pages similar to yours. For your own pages, you can use http://www.webconfs.com/similar-page-checker.php

Note: I don't know a tool that compares complete sites, but since search engines list pages, and not sites, you should address this on a page-by-page basis.

don't do mirror, at least you change something, otherwise it will be very easy to get banned

Thank you for your valuable openion as well as providing good source also.