I am thinking about hosting my own nameservers.
Two different IPs are required for this, and generally it is expected that these will be two different machines because downtime of one's DNS nameservers is evidently "bad".
But I can't find anywhere that will actually tell me the consequences.
If I am running a number of domains on a single server that has close to 100% uptime, is it really a big deal if I run my nameserver on that machine (I have two+ IP addresses that point to that server).
Can someone tell me what the worst case failure is, apart from possibly the DNS being down for a few hours after a downtime for the machine?
If all your name servers are unavailable for a longer period than your zone TTL, your zone will disappear from the Internet. Until at least one name server is brought back online, the zone will not exist. Mail sent to your domain will bounce, attempts to reach your web servers will make the browser go "Nope, no such site" and so on.
Since most people have a domain because they want to use it for something, it ceasing to exist is generally regarded as a problem.