Recently my DNS provider began experiencing a DNS amplification denial of service attack. This resulted in all of my websites being down for a period of about two days. In an attempt to prevent this type of problem from impacting my websites in the future I have now added two backup DNS providers. When a DNS server fails, the query is attempted on other servers on the list until one works. I am hopeful that this will reduce the impact of any future attacks.
As a general rule domains may utilize up to thirteenth servers, and as I was only using five there was plenty of room for improvement. The root zone uses twelve separate providers for its thirteen servers, and while my domains are not as critical there is technical advantage to removing all possible single points of failure. Perhaps having two backups is paranoid, but it will allow me to use all thirteenth name server spaces on my domains.