Backup DNS & SE penalty

do SEs penalize backup DNS?

[CdCardMain]

I am planning to host my sites on two independent hosts and change my DNS info to ns1.primaryhost.com and ns2.otherHost.com. This way, if the ns1. host fails then ns2. host can be redirected automatically. Is this plan going to work? How about the SEs? Do they penalize the site that has same contents on two different hosts? It's just one domain hosted on two independent hosting companies for backup purpose. I know Google cash IPs but I am not sure if they cash secondary IPs also. If they do, do they crawl secondary web sites and penalize if the contents are the same? You masters, could you please give some advice?

[ciml]

It should work well for most users other than search engines, but for the robots there remains a problem. They remember DNS information for much longer than normal browsers and ISP proxy caches.

If Google check the DNS when the server is up, and then try to crawl it when it is down, you still have a problem.