domain name system - Why should one have a secondary DNS server?

I'm very confused.

I basically understand how DNS works. Here's an example that helps illustrate what I'm having trouble understanding.

Right now, I run a small web-server. I use my provider's DNS manager, so I don't have a DNS server hosted on the machine.

Let's say for a second, that I don't use my host's DNS, and I decide to set up a DNS server on my server. Hypothetical scenario: my server (entire) server goes down - DNS included. Why do I need backup DNS? If the server is down, who cares if the DNS server is down too, considering that even if I had DNS up (it wasn't on the crashed server), it wouldn't be able to forward requests anyway since the server would be down?

Is the point of having secondary DNS, to be able to change the IP addresses that your DNS server points to, so if your webserver was down, you could redirect traffic to a backup? How would you switch to the secondary provider, in the event that your main DNS provider becomes unavailable? Is a backup DNS system basically up all the time? How is it configured? Is it just an exact clone of the DNS server you would have on your server? Do they run simultaneously?

Hopefully someone can see what I'm hung up on, and provide some guidance.

Answer

The major point in having a secondary DNS server is as backup in the event the primary DNS server handling your domain goes down. In this case, your server would be still up, and so without having a backup, nobody could get to your server possibly costing you lots of lost customers (i.e. REAL MONEY).

A secondary DNS server is always up, and ready to serve. It can help balance the load on the network as there are now more than one authoritative place to get your information. Updates are generally performed automatically from the master DNS. Thus it is an exact clone of the master.

Generally a DNS server contains more information than just a single server, it might contain mail routing information, information for many many hosts, mail spam keys, etc. So resilancy and redundancy are of DEFINITE benefit to domain holders.

I hope this helps your understanding.