Select a root server at the bottom. Some, but not all, have a "statistics" link. Seems to be stated in qps and message size distribution, but you should be able to derive traffic volume from that.
Assuming the mean is close to the median, they are reporting ~10B requests daily with a median response size of around 1KB. 10TB daily is a little under 1Gpbs. Traffic is spiky, but this isn't particularly complex once you consider they have multiple data centers/servers. Of course, I may have misread something as daily that was hourly or something like that...
So it looks like the root namespace providers output a totally reasonable amount of traffic. Divided between the hundreds of points of presence globally, this is tens of megabits per physical host.
The servers themselves are ordinary 1 RU physical rack mount servers with 1 Gbps or 10 Gbps Ethernet. Nothing special. I'm guessing that most of the load isn't from the root, e.g.: "j.root-servers.net", but from hosting the authoritative DNS servers for .com and .net (b.gtld-servers.net) on the same box. That would surely have more traffic and much more data.
I havent looked in a good 5 years, but “not much.” There were roots running off of 1gbs links back then. A quick loot at the sibling comment root stats and Im swagging a few hundred thousand tps at about 256 bytes per response. The problem is/was mostly in distributing and sinking inbound garbage packets.
You can also click on the "RSSAC" button on root-servers.org to get the YAML straight from the root server operators themselves.
Most of the root server operators have anycast instances deployed in organizations that host the servers for them. So there's not an easy way to measure bandwidth utilization because many root server anycast instances are hosted in organizations that may not, or could not, report that bandwidth utilization. Look at the map on root-servers.org to see how dispersed around the world these things are.
