If my main server go offline for some reason for +1hrs, I'm planning to make a DNS change so users will access secondary server. It is not a perfect solution to decrease downtime but it is simple and would work. I'm not sure about its usefulness. So I have a question. If I'm going to make a DNS change to an A record for my domain (changing from one IP to another), what percentage of users are moved over to the new info in 2hrs? (roughly) I know this is a vague question and there are lots of variables but any input is welcomed because I had painful downtime experiences and don't want to experience it again. Thanks