LifeinAsia - 6:19 pm on Feb 13, 2013 (gmt 0)
G or B goes to index a page on regular site A, something catastrophic happens, and now requests are being directed to site B.
Why would site B be different from site A? It should be the exact same domain name, only the IP address is different. Users (and G/B) will still be going to example.com, regardless of whether that domain name resolved to IP a.b.c.d or IP w.x.y.z. (Ideally, the content will be the exact same as well, although of course it may be slightly out of date, depending on how often the failover site gets updated.) This is pretty much standard.