> You should use a network topology strategy with high RF in each DC
There's some debate here - some blogs/speakers will say to put a replica on each instance, but that falls down above a few dozen instances. Imagine if you have (for example) 200 instances per DC, auth logins for super users is 101 replicas serving the read - that's a really slow login that's likely to fail (think about thread pools on the coordinator doing the read response handling, it's an ugly ugly mess). Normal logins do use LOCAL_ONE though so if there are lots of replicas, auth will be faster - so use 5-10 replicas per DC, and crank up the caching timeouts as well
